diff --git a/composer.json b/composer.json
index b85a240..1d0afbc 100644
--- a/composer.json
+++ b/composer.json
@@ -49,6 +49,5 @@
         "preferred-install": "dist",
         "sort-packages": true
     },
-    "minimum-stability": "dev",
     "prefer-stable": true
 }
diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 1f818db..8b1e721 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -78,162 +78,6 @@ parameters:
 			count: 1
 			path: src/Gitonomy/Git/Blame/Line.php
 
-		-
-			message: '#^Method Gitonomy\\Git\\Blob\:\:getContent\(\) should return string but returns string\|null\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Blob.php
-
-		-
-			message: '#^Argument of an invalid type mixed supplied for foreach, only iterables are supported\.$#'
-			identifier: foreach.nonIterable
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:__construct\(\) has parameter \$data with no value type specified in iterable type array\.$#'
-			identifier: missingType.iterableValue
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getAuthorDate\(\) should return DateTime but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getAuthorEmail\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getAuthorName\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getBodyMessage\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getCommitterDate\(\) should return DateTime but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getCommitterEmail\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getCommitterName\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getMessage\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getParentHashes\(\) should return array\<string\> but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getShortHash\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getShortMessage\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getSubjectMessage\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getTree\(\) should return Gitonomy\\Git\\Tree but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:getTreeHash\(\) should return string but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Commit\:\:setData\(\) has parameter \$data with no value type specified in iterable type array\.$#'
-			identifier: missingType.iterableValue
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Parameter \#1 \$hash of method Gitonomy\\Git\\Repository\:\:getCommit\(\) expects string, mixed given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Parameter \#1 \$hash of method Gitonomy\\Git\\Repository\:\:getTree\(\) expects string, mixed given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Parameter \#1 \$haystack of static method Gitonomy\\Git\\Util\\StringHelper\:\:strpos\(\) expects string, mixed given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Parameter \#1 \$rawDiff of static method Gitonomy\\Git\\Diff\\Diff\:\:parse\(\) expects string, string\|null given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Parameter \#1 \$string of function trim expects string, string\|null given\.$#'
-			identifier: argument.type
-			count: 2
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Parameter \#1 \$string of static method Gitonomy\\Git\\Util\\StringHelper\:\:strlen\(\) expects string, mixed given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Parameter \#1 \$string of static method Gitonomy\\Git\\Util\\StringHelper\:\:substr\(\) expects string, mixed given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/Commit.php
-
-		-
-			message: '#^Parameter \#2 \$string of function explode expects string, mixed given\.$#'
-			identifier: argument.type
-			count: 2
-			path: src/Gitonomy/Git/Commit.php
-
 		-
 			message: '#^Method Gitonomy\\Git\\Diff\\Diff\:\:fromArray\(\) has parameter \$array with no value type specified in iterable type array\.$#'
 			identifier: missingType.iterableValue
@@ -336,72 +180,12 @@ parameters:
 			count: 1
 			path: src/Gitonomy/Git/Parser/ParserBase.php
 
-		-
-			message: '#^Parameter \#1 \$string of function trim expects string, string\|null given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/PushReference.php
-
-		-
-			message: '#^Parameter \#1 \$string of function trim expects string, string\|null given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/Reference.php
-
 		-
 			message: '#^Method Gitonomy\\Git\\Reference\\Branch\:\:isLocal\(\) should return bool but returns bool\|null\.$#'
 			identifier: return.type
 			count: 1
 			path: src/Gitonomy/Git/Reference/Branch.php
 
-		-
-			message: '#^Method Gitonomy\\Git\\Reference\\Tag\:\:getBodyMessage\(\) should return string\|false but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Reference/Tag.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Reference\\Tag\:\:getGPGSignature\(\) should return string\|false but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Reference/Tag.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Reference\\Tag\:\:getMessage\(\) should return string\|false but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Reference/Tag.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Reference\\Tag\:\:getSubjectMessage\(\) should return string\|false but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Reference/Tag.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Reference\\Tag\:\:getTaggerDate\(\) should return DateTime\|false but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Reference/Tag.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Reference\\Tag\:\:getTaggerEmail\(\) should return string\|false but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Reference/Tag.php
-
-		-
-			message: '#^Method Gitonomy\\Git\\Reference\\Tag\:\:getTaggerName\(\) should return string\|false but returns mixed\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Gitonomy/Git/Reference/Tag.php
-
-		-
-			message: '#^Parameter \#2 \$string of function explode expects string, mixed given\.$#'
-			identifier: argument.type
-			count: 2
-			path: src/Gitonomy/Git/Reference/Tag.php
-
 		-
 			message: '#^Class Gitonomy\\Git\\ReferenceBag implements generic interface IteratorAggregate but does not specify its types\: TKey, TValue$#'
 			identifier: missingType.generics
@@ -468,12 +252,6 @@ parameters:
 			count: 1
 			path: src/Gitonomy/Git/Repository.php
 
-		-
-			message: '#^Parameter \#1 \$rawDiff of static method Gitonomy\\Git\\Diff\\Diff\:\:parse\(\) expects string, string\|null given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/Repository.php
-
 		-
 			message: '#^Parameter \#1 \$string of function trim expects string, string\|false given\.$#'
 			identifier: argument.type
@@ -521,15 +299,3 @@ parameters:
 			identifier: missingType.iterableValue
 			count: 1
 			path: src/Gitonomy/Git/WorkingCopy.php
-
-		-
-			message: '#^Parameter \#1 \$rawDiff of static method Gitonomy\\Git\\Diff\\Diff\:\:parse\(\) expects string, string\|null given\.$#'
-			identifier: argument.type
-			count: 2
-			path: src/Gitonomy/Git/WorkingCopy.php
-
-		-
-			message: '#^Parameter \#2 \$string of function explode expects string, string\|null given\.$#'
-			identifier: argument.type
-			count: 1
-			path: src/Gitonomy/Git/WorkingCopy.php
diff --git a/src/Gitonomy/Git/Admin.php b/src/Gitonomy/Git/Admin.php
index 024acf4..35d4875 100644
--- a/src/Gitonomy/Git/Admin.php
+++ b/src/Gitonomy/Git/Admin.php
@@ -37,7 +37,7 @@ public static function init(string $path, bool $bare = true, array $options = []
 
         $process->run();
 
-        if (!$process->isSuccessFul()) {
+        if (!$process->isSuccessful()) {
             throw new RuntimeException(\sprintf("Error on repository initialization, command wasn't successful (%s). Error output:\n%s", $process->getCommandLine(), $process->getErrorOutput()));
         }
 
@@ -62,7 +62,7 @@ public static function isValidRepository(string $url, array $options = []): bool
 
         $process->run();
 
-        return $process->isSuccessFul();
+        return $process->isSuccessful();
     }
 
     /**
@@ -86,7 +86,7 @@ public static function isValidRepositoryAndBranch(string $url, string $branchNam
         $process->run();
         $processOutput = $process->getOutput();
 
-        return $process->isSuccessFul() && str_contains($processOutput, $branchName);
+        return $process->isSuccessful() && str_contains($processOutput, $branchName);
     }
 
     /**
@@ -149,7 +149,7 @@ public static function cloneRepository(string $path, string $url, array $args =
 
         $process->run();
 
-        if (!$process->isSuccessFul()) {
+        if (!$process->isSuccessful()) {
             throw new RuntimeException(\sprintf('Error while initializing repository: %s', $process->getErrorOutput()));
         }
 
diff --git a/src/Gitonomy/Git/Blob.php b/src/Gitonomy/Git/Blob.php
index 54a9c22..60555cb 100644
--- a/src/Gitonomy/Git/Blob.php
+++ b/src/Gitonomy/Git/Blob.php
@@ -12,6 +12,8 @@
 
 namespace Gitonomy\Git;
 
+use Gitonomy\Git\Exception\ReferenceNotFoundException;
+
 /**
  * Representation of a Blob commit.
  *
@@ -53,7 +55,12 @@ public function getHash(): string
     public function getContent(): string
     {
         if (null === $this->content) {
-            $this->content = $this->repository->run('cat-file', ['-p', $this->hash]);
+            $content = $this->repository->run('cat-file', ['-p', $this->hash]);
+            if (null === $content) {
+                throw new ReferenceNotFoundException($this->hash);
+            }
+
+            $this->content = $content;
         }
 
         return $this->content;
diff --git a/src/Gitonomy/Git/Commit.php b/src/Gitonomy/Git/Commit.php
index 671f467..2e0215f 100644
--- a/src/Gitonomy/Git/Commit.php
+++ b/src/Gitonomy/Git/Commit.php
@@ -27,15 +27,36 @@
 final class Commit extends Revision
 {
     /**
-     * Associative array of commit data.
-     *
-     * @var array<string, mixed>
+     * Whether the fields below have been populated (either lazily fetched
+     * from the repository, or provided upfront through setData()).
+     */
+    private bool $loaded = false;
+
+    private ?string $treeHash = null;
+
+    /**
+     * @var string[]|null
      */
-    private array $data = [];
+    private ?array $parentHashes = null;
+
+    private ?string $authorName = null;
+    private ?string $authorEmail = null;
+    private ?\DateTime $authorDate = null;
+    private ?string $committerName = null;
+    private ?string $committerEmail = null;
+    private ?\DateTime $committerDate = null;
+    private ?string $message = null;
+
+    // Values derived from the fields above, computed and cached independently.
+    private ?string $shortHash = null;
+    private ?Tree $tree = null;
+    private ?string $subjectMessage = null;
+    private ?string $bodyMessage = null;
 
     /**
-     * @param Repository $repository Repository of the commit
-     * @param string     $hash       Hash of the commit
+     * @param Repository           $repository Repository of the commit
+     * @param string               $hash       Hash of the commit
+     * @param array<string, mixed> $data
      */
     public function __construct(Repository $repository, string $hash, array $data = [])
     {
@@ -48,10 +69,28 @@ public function __construct(Repository $repository, string $hash, array $data =
         $this->setData($data);
     }
 
+    /**
+     * @param array<string, mixed> $data
+     */
     public function setData(array $data): void
     {
         foreach ($data as $name => $value) {
-            $this->data[$name] = $value;
+            match ($name) {
+                'treeHash' => $this->treeHash = self::asString($name, $value),
+                'parentHashes' => $this->parentHashes = self::asStringList($name, $value),
+                'authorName' => $this->authorName = self::asString($name, $value),
+                'authorEmail' => $this->authorEmail = self::asString($name, $value),
+                'authorDate' => $this->authorDate = self::asDateTime($name, $value),
+                'committerName' => $this->committerName = self::asString($name, $value),
+                'committerEmail' => $this->committerEmail = self::asString($name, $value),
+                'committerDate' => $this->committerDate = self::asDateTime($name, $value),
+                'message' => $this->message = self::asString($name, $value),
+                default => throw new InvalidArgumentException(\sprintf('Unknown commit data "%s".', $name)),
+            };
+        }
+
+        if ([] !== $data) {
+            $this->loaded = true;
         }
     }
 
@@ -59,7 +98,12 @@ public function getDiff(): Diff
     {
         $args = ['-r', '-p', '--raw', '-m', '-M', '--no-commit-id', '--full-index', $this->revision];
 
-        $diff = Diff::parse($this->repository->run('diff-tree', $args));
+        $result = $this->repository->run('diff-tree', $args);
+        if (null === $result) {
+            throw new ReferenceNotFoundException($this->revision);
+        }
+
+        $diff = Diff::parse($result);
         $diff->setRepository($this->repository);
 
         return $diff;
@@ -78,7 +122,16 @@ public function getHash(): string
      */
     public function getShortHash(): string
     {
-        return $this->getData('shortHash');
+        if (null === $this->shortHash) {
+            $result = $this->repository->run('log', ['--abbrev-commit', '--format=%h', '-n', 1, $this->revision]);
+            if (null === $result) {
+                throw new ReferenceNotFoundException($this->revision);
+            }
+
+            $this->shortHash = trim($result);
+        }
+
+        return $this->shortHash;
     }
 
     /**
@@ -96,7 +149,9 @@ public function getFixedShortHash(int $length = 6): string
      */
     public function getParentHashes(): array
     {
-        return $this->getData('parentHashes');
+        $this->ensureLoaded();
+
+        return $this->parentHashes ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     /**
@@ -107,7 +162,7 @@ public function getParentHashes(): array
     public function getParents(): array
     {
         $result = [];
-        foreach ($this->getData('parentHashes') as $parentHash) {
+        foreach ($this->getParentHashes() as $parentHash) {
             $result[] = $this->repository->getCommit($parentHash);
         }
 
@@ -119,12 +174,18 @@ public function getParents(): array
      */
     public function getTreeHash(): string
     {
-        return $this->getData('treeHash');
+        $this->ensureLoaded();
+
+        return $this->treeHash ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     public function getTree(): Tree
     {
-        return $this->getData('tree');
+        if (null === $this->tree) {
+            $this->tree = $this->repository->getTree($this->getTreeHash());
+        }
+
+        return $this->tree;
     }
 
     public function getLastModification(?string $path = null): self
@@ -139,6 +200,10 @@ public function getLastModification(?string $path = null): self
 
         $result = $this->repository->run('log', ['--format=%H', '-n', 1, $this->revision, '--', $path]);
 
+        if (null === $result) {
+            throw new ReferenceNotFoundException($this->revision);
+        }
+
         return $this->repository->getCommit(trim($result));
     }
 
@@ -149,7 +214,7 @@ public function getLastModification(?string $path = null): self
      */
     public function getShortMessage(int $length = 50, bool $preserve = false, string $separator = '...'): string
     {
-        $message = $this->getData('subjectMessage');
+        $message = $this->getSubjectMessage();
 
         if (StringHelper::strlen($message) > $length) {
             if ($preserve && false !== ($breakpoint = StringHelper::strpos($message, ' ', $length))) {
@@ -229,7 +294,9 @@ public function getIncludingBranches(bool $local = true, bool $remote = true): a
      */
     public function getAuthorName(): string
     {
-        return $this->getData('authorName');
+        $this->ensureLoaded();
+
+        return $this->authorName ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     /**
@@ -237,7 +304,9 @@ public function getAuthorName(): string
      */
     public function getAuthorEmail(): string
     {
-        return $this->getData('authorEmail');
+        $this->ensureLoaded();
+
+        return $this->authorEmail ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     /**
@@ -245,7 +314,9 @@ public function getAuthorEmail(): string
      */
     public function getAuthorDate(): \DateTime
     {
-        return $this->getData('authorDate');
+        $this->ensureLoaded();
+
+        return $this->authorDate ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     /**
@@ -253,7 +324,9 @@ public function getAuthorDate(): \DateTime
      */
     public function getCommitterName(): string
     {
-        return $this->getData('committerName');
+        $this->ensureLoaded();
+
+        return $this->committerName ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     /**
@@ -261,7 +334,9 @@ public function getCommitterName(): string
      */
     public function getCommitterEmail(): string
     {
-        return $this->getData('committerEmail');
+        $this->ensureLoaded();
+
+        return $this->committerEmail ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     /**
@@ -269,7 +344,9 @@ public function getCommitterEmail(): string
      */
     public function getCommitterDate(): \DateTime
     {
-        return $this->getData('committerDate');
+        $this->ensureLoaded();
+
+        return $this->committerDate ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     /**
@@ -277,7 +354,9 @@ public function getCommitterDate(): \DateTime
      */
     public function getMessage(): string
     {
-        return $this->getData('message');
+        $this->ensureLoaded();
+
+        return $this->message ?? throw new ReferenceNotFoundException($this->revision);
     }
 
     /**
@@ -285,7 +364,12 @@ public function getMessage(): string
      */
     public function getSubjectMessage(): string
     {
-        return $this->getData('subjectMessage');
+        if (null === $this->subjectMessage) {
+            $lines = explode("\n", $this->getMessage());
+            $this->subjectMessage = reset($lines);
+        }
+
+        return $this->subjectMessage;
     }
 
     /**
@@ -293,7 +377,16 @@ public function getSubjectMessage(): string
      */
     public function getBodyMessage(): string
     {
-        return $this->getData('bodyMessage');
+        if (null === $this->bodyMessage) {
+            $lines = explode("\n", $this->getMessage());
+
+            array_shift($lines);
+            array_shift($lines);
+
+            $this->bodyMessage = implode("\n", $lines);
+        }
+
+        return $this->bodyMessage;
     }
 
     public function getCommit(): self
@@ -301,68 +394,75 @@ public function getCommit(): self
         return $this;
     }
 
-    private function getData(string $name): mixed
+    private function ensureLoaded(): void
     {
-        if (isset($this->data[$name])) {
-            return $this->data[$name];
-        }
-
-        if ('shortHash' === $name) {
-            $this->data['shortHash'] = trim($this->repository->run('log', ['--abbrev-commit', '--format=%h', '-n', 1, $this->revision]));
-
-            return $this->data['shortHash'];
+        if ($this->loaded) {
+            return;
         }
 
-        if ('tree' === $name) {
-            $this->data['tree'] = $this->repository->getTree($this->getData('treeHash'));
+        $parser = new Parser\CommitParser();
 
-            return $this->data['tree'];
+        try {
+            $result = $this->repository->run('cat-file', ['commit', $this->revision]);
+        } catch (ProcessException $e) {
+            throw new ReferenceNotFoundException(\sprintf('Can not find reference "%s"', $this->revision));
         }
 
-        if ('subjectMessage' === $name) {
-            $lines = explode("\n", $this->getData('message'));
-            $this->data['subjectMessage'] = reset($lines);
-
-            return $this->data['subjectMessage'];
+        if (null === $result) {
+            throw new ReferenceNotFoundException(\sprintf('Can not find reference "%s"', $this->revision));
         }
 
-        if ('bodyMessage' === $name) {
-            $message = $this->getData('message');
+        $parser->parse($result);
 
-            $lines = explode("\n", $message);
+        $this->treeHash = $parser->tree;
+        $this->parentHashes = $parser->parents;
+        $this->authorName = $parser->authorName;
+        $this->authorEmail = $parser->authorEmail;
+        $this->authorDate = $parser->authorDate;
+        $this->committerName = $parser->committerName;
+        $this->committerEmail = $parser->committerEmail;
+        $this->committerDate = $parser->committerDate;
+        $this->message = $parser->message;
+
+        $this->loaded = true;
+    }
 
-            array_shift($lines);
-            array_shift($lines);
+    private static function asString(string $name, mixed $value): string
+    {
+        if (!\is_string($value)) {
+            throw new InvalidArgumentException(\sprintf('Commit data "%s" must be a string.', $name));
+        }
 
-            $this->data['bodyMessage'] = implode("\n", $lines);
+        return $value;
+    }
 
-            return $this->data['bodyMessage'];
+    private static function asDateTime(string $name, mixed $value): \DateTime
+    {
+        if (!$value instanceof \DateTime) {
+            throw new InvalidArgumentException(\sprintf('Commit data "%s" must be a DateTime.', $name));
         }
 
-        $parser = new Parser\CommitParser();
+        return $value;
+    }
 
-        try {
-            $result = $this->repository->run('cat-file', ['commit', $this->revision]);
-        } catch (ProcessException $e) {
-            throw new ReferenceNotFoundException(\sprintf('Can not find reference "%s"', $this->revision));
+    /**
+     * @return string[]
+     */
+    private static function asStringList(string $name, mixed $value): array
+    {
+        if (!\is_array($value)) {
+            throw new InvalidArgumentException(\sprintf('Commit data "%s" must be an array.', $name));
         }
 
-        $parser->parse($result);
+        $result = [];
+        foreach ($value as $item) {
+            if (!\is_string($item)) {
+                throw new InvalidArgumentException(\sprintf('Commit data "%s" must be an array of strings.', $name));
+            }
 
-        $this->data['treeHash'] = $parser->tree;
-        $this->data['parentHashes'] = $parser->parents;
-        $this->data['authorName'] = $parser->authorName;
-        $this->data['authorEmail'] = $parser->authorEmail;
-        $this->data['authorDate'] = $parser->authorDate;
-        $this->data['committerName'] = $parser->committerName;
-        $this->data['committerEmail'] = $parser->committerEmail;
-        $this->data['committerDate'] = $parser->committerDate;
-        $this->data['message'] = $parser->message;
-
-        if (!isset($this->data[$name])) {
-            throw new \InvalidArgumentException(\sprintf('No data named "%s" in Commit.', $name));
+            $result[] = $item;
         }
 
-        return $this->data[$name];
+        return $result;
     }
 }
diff --git a/src/Gitonomy/Git/Hooks.php b/src/Gitonomy/Git/Hooks.php
index f07bf3b..6b6835c 100644
--- a/src/Gitonomy/Git/Hooks.php
+++ b/src/Gitonomy/Git/Hooks.php
@@ -93,7 +93,7 @@ public function set(string $name, string $content): void
 
         $path = $this->getPath($name);
         file_put_contents($path, $content);
-        chmod($path, 0o777);
+        chmod($path, 0o700);
     }
 
     /**
diff --git a/src/Gitonomy/Git/PushReference.php b/src/Gitonomy/Git/PushReference.php
index dc3086e..e7ca21f 100644
--- a/src/Gitonomy/Git/PushReference.php
+++ b/src/Gitonomy/Git/PushReference.php
@@ -117,6 +117,11 @@ private function getForce(): bool
             $this->after,
         ]);
 
+        if (null === $result) {
+            // No common ancestor could be established: treat it as a force update.
+            return true;
+        }
+
         return $this->before !== trim($result);
     }
 }
diff --git a/src/Gitonomy/Git/Reference.php b/src/Gitonomy/Git/Reference.php
index 885335a..869e5b9 100644
--- a/src/Gitonomy/Git/Reference.php
+++ b/src/Gitonomy/Git/Reference.php
@@ -54,6 +54,10 @@ public function getCommitHash(): string
             throw new ReferenceNotFoundException(\sprintf('Can not find revision "%s"', $this->revision));
         }
 
+        if (null === $result) {
+            throw new ReferenceNotFoundException(\sprintf('Can not find revision "%s"', $this->revision));
+        }
+
         return $this->commitHash = trim($result);
     }
 
diff --git a/src/Gitonomy/Git/Reference/Tag.php b/src/Gitonomy/Git/Reference/Tag.php
index 2953938..b07076d 100644
--- a/src/Gitonomy/Git/Reference/Tag.php
+++ b/src/Gitonomy/Git/Reference/Tag.php
@@ -27,10 +27,17 @@
  */
 final class Tag extends Reference
 {
-    /**
-     * @var array<string, mixed>|null
-     */
-    private ?array $data = null;
+    private bool $loaded = false;
+
+    private ?string $taggerName = null;
+    private ?string $taggerEmail = null;
+    private ?\DateTime $taggerDate = null;
+    private ?string $message = null;
+    private ?string $gpgSignature = null;
+
+    // Values derived from the fields above, computed and cached independently.
+    private ?string $subjectMessage = null;
+    private ?string $bodyMessage = null;
 
     public function getName(): string
     {
@@ -47,12 +54,13 @@ public function getName(): string
     public function isAnnotated(): bool
     {
         try {
-            $this->repository->run('cat-file', ['tag', $this->revision]);
+            $result = $this->repository->run('cat-file', ['tag', $this->revision]);
         } catch (ProcessException $e) {
             return false; // Is not an annotated tag
         }
 
-        return true;
+        // In non-debug mode, a failed command returns null instead of throwing.
+        return null !== $result;
     }
 
     /**
@@ -87,7 +95,12 @@ public function getCommit(): Commit
      */
     public function getTaggerName(): string|false
     {
-        return $this->getData('taggerName');
+        if (!$this->isAnnotated()) {
+            return false;
+        }
+        $this->ensureLoaded();
+
+        return $this->taggerName ?? throw new \InvalidArgumentException('No data named "taggerName" in Tag.');
     }
 
     /**
@@ -95,7 +108,12 @@ public function getTaggerName(): string|false
      */
     public function getTaggerEmail(): string|false
     {
-        return $this->getData('taggerEmail');
+        if (!$this->isAnnotated()) {
+            return false;
+        }
+        $this->ensureLoaded();
+
+        return $this->taggerEmail ?? throw new \InvalidArgumentException('No data named "taggerEmail" in Tag.');
     }
 
     /**
@@ -103,7 +121,12 @@ public function getTaggerEmail(): string|false
      */
     public function getTaggerDate(): \DateTime|false
     {
-        return $this->getData('taggerDate');
+        if (!$this->isAnnotated()) {
+            return false;
+        }
+        $this->ensureLoaded();
+
+        return $this->taggerDate ?? throw new \InvalidArgumentException('No data named "taggerDate" in Tag.');
     }
 
     /**
@@ -111,7 +134,12 @@ public function getTaggerDate(): \DateTime|false
      */
     public function getMessage(): string|false
     {
-        return $this->getData('message');
+        if (!$this->isAnnotated()) {
+            return false;
+        }
+        $this->ensureLoaded();
+
+        return $this->message ?? throw new \InvalidArgumentException('No data named "message" in Tag.');
     }
 
     /**
@@ -119,7 +147,16 @@ public function getMessage(): string|false
      */
     public function getSubjectMessage(): string|false
     {
-        return $this->getData('subjectMessage');
+        if (!$this->isAnnotated()) {
+            return false;
+        }
+
+        if (null === $this->subjectMessage) {
+            $lines = explode("\n", $this->getMessageOrThrow());
+            $this->subjectMessage = reset($lines);
+        }
+
+        return $this->subjectMessage;
     }
 
     /**
@@ -127,7 +164,27 @@ public function getSubjectMessage(): string|false
      */
     public function getBodyMessage(): string|false
     {
-        return $this->getData('bodyMessage');
+        if (!$this->isAnnotated()) {
+            return false;
+        }
+
+        if (null === $this->bodyMessage) {
+            $lines = explode("\n", $this->getMessageOrThrow());
+
+            // Drop the subject line, then the blank separator line if the
+            // message follows the "subject\n\nbody" convention.
+            array_shift($lines);
+            if (isset($lines[0]) && '' === $lines[0]) {
+                array_shift($lines);
+            }
+            if ([] !== $lines && '' === end($lines)) {
+                array_pop($lines);
+            }
+
+            $this->bodyMessage = implode("\n", $lines);
+        }
+
+        return $this->bodyMessage;
     }
 
     /**
@@ -135,7 +192,12 @@ public function getBodyMessage(): string|false
      */
     public function getGPGSignature(): string|false
     {
-        return $this->getData('gpgSignature');
+        if (!$this->isAnnotated()) {
+            return false;
+        }
+        $this->ensureLoaded();
+
+        return $this->gpgSignature ?? throw new \InvalidArgumentException('No data named "gpgSignature" in Tag.');
     }
 
     /**
@@ -152,51 +214,34 @@ public function isSigned(): bool
         }
     }
 
-    private function getData(string $name): mixed
+    private function getMessageOrThrow(): string
     {
-        if (!$this->isAnnotated()) {
-            return false;
-        }
+        $this->ensureLoaded();
 
-        if (isset($this->data[$name])) {
-            return $this->data[$name];
-        }
-
-        if ('subjectMessage' === $name) {
-            $lines = explode("\n", $this->getData('message'));
-            $this->data['subjectMessage'] = reset($lines);
-
-            return $this->data['subjectMessage'];
-        }
-
-        if ('bodyMessage' === $name) {
-            $message = $this->getData('message');
-
-            $lines = explode("\n", $message);
-
-            array_shift($lines);
-            array_pop($lines);
-
-            $this->data['bodyMessage'] = implode("\n", $lines);
+        return $this->message ?? throw new \InvalidArgumentException('No data named "message" in Tag.');
+    }
 
-            return $this->data['bodyMessage'];
+    private function ensureLoaded(): void
+    {
+        if ($this->loaded) {
+            return;
         }
 
         $parser = new TagParser();
         $result = $this->repository->run('cat-file', ['tag', $this->revision]);
 
-        $parser->parse($result);
+        if (null === $result) {
+            throw new \InvalidArgumentException('Unable to read tag data.');
+        }
 
-        $this->data['taggerName'] = $parser->taggerName;
-        $this->data['taggerEmail'] = $parser->taggerEmail;
-        $this->data['taggerDate'] = $parser->taggerDate;
-        $this->data['message'] = $parser->message;
-        $this->data['gpgSignature'] = $parser->gpgSignature;
+        $parser->parse($result);
 
-        if (!isset($this->data[$name])) {
-            throw new \InvalidArgumentException(\sprintf('No data named "%s" in Tag.', $name));
-        }
+        $this->taggerName = $parser->taggerName;
+        $this->taggerEmail = $parser->taggerEmail;
+        $this->taggerDate = $parser->taggerDate;
+        $this->message = $parser->message;
+        $this->gpgSignature = $parser->gpgSignature;
 
-        return $this->data[$name];
+        $this->loaded = true;
     }
 }
diff --git a/src/Gitonomy/Git/ReferenceBag.php b/src/Gitonomy/Git/ReferenceBag.php
index b1833b3..e5408ad 100644
--- a/src/Gitonomy/Git/ReferenceBag.php
+++ b/src/Gitonomy/Git/ReferenceBag.php
@@ -145,9 +145,8 @@ public function hasTag(string $name): bool
     public function getFirstBranch(): Reference|false
     {
         $this->initialize();
-        reset($this->branches);
 
-        return current($this->references);
+        return reset($this->branches);
     }
 
     /**
diff --git a/src/Gitonomy/Git/Repository.php b/src/Gitonomy/Git/Repository.php
index ca480f3..3e49988 100644
--- a/src/Gitonomy/Git/Repository.php
+++ b/src/Gitonomy/Git/Repository.php
@@ -361,7 +361,12 @@ public function getDiff(RevisionList|Revision|string|array|null $revisions): Dif
 
         $args = array_merge(['-r', '-p', '--raw', '-m', '-M', '--no-commit-id', '--full-index'], $revisions->getAsTextArray());
 
-        $diff = Diff::parse($this->run('diff', $args));
+        $result = $this->run('diff', $args);
+        if (null === $result) {
+            throw new RuntimeException('Unable to compute diff.');
+        }
+
+        $diff = Diff::parse($result);
         $diff->setRepository($this);
 
         return $diff;
@@ -393,7 +398,7 @@ public function getSize(): int
      */
     public function shell(string $command, array $env = []): void
     {
-        $argument = \sprintf('%s \'%s\'', $command, $this->gitDir);
+        $argument = \sprintf('%s %s', $command, escapeshellarg($this->gitDir));
 
         $prefix = '';
         foreach ($env as $name => $value) {
diff --git a/src/Gitonomy/Git/WorkingCopy.php b/src/Gitonomy/Git/WorkingCopy.php
index e48acd9..aa96d52 100644
--- a/src/Gitonomy/Git/WorkingCopy.php
+++ b/src/Gitonomy/Git/WorkingCopy.php
@@ -15,6 +15,7 @@
 use Gitonomy\Git\Diff\Diff;
 use Gitonomy\Git\Exception\InvalidArgumentException;
 use Gitonomy\Git\Exception\LogicException;
+use Gitonomy\Git\Exception\RuntimeException;
 
 /**
  * @author Alexandre Salomé <alexandre.salome@gmail.com>
@@ -34,7 +35,12 @@ public function __construct(
      */
     public function getUntrackedFiles(): array
     {
-        $lines = explode("\0", $this->run('status', ['--porcelain', '--untracked-files=all', '-z']));
+        $output = $this->run('status', ['--porcelain', '--untracked-files=all', '-z']);
+        if (null === $output) {
+            return [];
+        }
+
+        $lines = explode("\0", $output);
         $lines = array_filter($lines, static function ($l) {
             return '?? ' === substr($l, 0, 3);
         });
@@ -46,7 +52,12 @@ public function getUntrackedFiles(): array
 
     public function getDiffPending(): Diff
     {
-        $diff = Diff::parse($this->run('diff', ['-r', '-p', '--raw', '-m', '-M', '--full-index']));
+        $result = $this->run('diff', ['-r', '-p', '--raw', '-m', '-M', '--full-index']);
+        if (null === $result) {
+            throw new RuntimeException('Unable to compute pending diff.');
+        }
+
+        $diff = Diff::parse($result);
         $diff->setRepository($this->repository);
 
         return $diff;
@@ -54,7 +65,12 @@ public function getDiffPending(): Diff
 
     public function getDiffStaged(): Diff
     {
-        $diff = Diff::parse($this->run('diff', ['-r', '-p', '--raw', '-m', '-M', '--full-index', '--staged']));
+        $result = $this->run('diff', ['-r', '-p', '--raw', '-m', '-M', '--full-index', '--staged']);
+        if (null === $result) {
+            throw new RuntimeException('Unable to compute staged diff.');
+        }
+
+        $diff = Diff::parse($result);
         $diff->setRepository($this->repository);
 
         return $diff;
diff --git a/tests/Gitonomy/Git/Tests/HooksTest.php b/tests/Gitonomy/Git/Tests/HooksTest.php
index 7256db1..b1ab8be 100644
--- a/tests/Gitonomy/Git/Tests/HooksTest.php
+++ b/tests/Gitonomy/Git/Tests/HooksTest.php
@@ -134,7 +134,7 @@ public function testSet(Repository $repository): void
         $this->assertEquals('bar', file_get_contents($file), 'Hook content is correct');
 
         $perms = fileperms($file);
-        $this->assertEquals(\defined('PHP_WINDOWS_VERSION_BUILD') ? 0o666 : 0o777, $perms & 0o777, 'Hook permissions are correct');
+        $this->assertEquals(\defined('PHP_WINDOWS_VERSION_BUILD') ? 0o666 : 0o700, $perms & 0o777, 'Hook permissions are correct');
     }
 
     #[DataProvider('provideFoobar')]
diff --git a/tests/Gitonomy/Git/Tests/ReferenceBagTest.php b/tests/Gitonomy/Git/Tests/ReferenceBagTest.php
index a626663..7278b19 100644
--- a/tests/Gitonomy/Git/Tests/ReferenceBagTest.php
+++ b/tests/Gitonomy/Git/Tests/ReferenceBagTest.php
@@ -12,11 +12,35 @@
 
 namespace Gitonomy\Git\Tests;
 
+use Gitonomy\Git\Reference\Branch;
 use Gitonomy\Git\Repository;
 use PHPUnit\Framework\Attributes\DataProvider;
 
 class ReferenceBagTest extends AbstractTestCase
 {
+    #[DataProvider('provideFoobar')]
+    public function testGetFirstBranch(Repository $repository): void
+    {
+        $branch = $repository->getReferences()->getFirstBranch();
+
+        $this->assertInstanceOf(Branch::class, $branch);
+    }
+
+    public function testGetFirstBranchWithNoBranches(): void
+    {
+        $repository = self::createFoobarRepository(false);
+        $wc = $repository->getWorkingCopy();
+        $wc->checkout('0.1');
+
+        foreach ($repository->getReferences()->getBranches() as $branch) {
+            $branch->delete();
+        }
+
+        $refs = $repository->getReferences(true);
+        $this->assertFalse($refs->hasBranches());
+        $this->assertFalse($refs->getFirstBranch(), 'getFirstBranch() must not return a non-branch reference');
+    }
+
     #[DataProvider('provideFoobar')]
     public function testUnknownReference(Repository $repository): void
     {
diff --git a/tests/Gitonomy/Git/Tests/ReferenceTest.php b/tests/Gitonomy/Git/Tests/ReferenceTest.php
index f164c34..55da2a5 100644
--- a/tests/Gitonomy/Git/Tests/ReferenceTest.php
+++ b/tests/Gitonomy/Git/Tests/ReferenceTest.php
@@ -70,6 +70,16 @@ public function testGetTag(Repository $repository): void
         $this->assertEquals(self::LONGFILE_COMMIT, $tag->getCommit()->getHash(), 'Commit hash is correct');
     }
 
+    #[DataProvider('provideFoobar')]
+    public function testIsAnnotatedIsFalseForLightweightTagWhenDebugIsFalse(Repository $repository): void
+    {
+        $repository = new Repository($repository->getPath(), array_merge(self::getOptions(), ['debug' => false]));
+
+        $tag = $repository->getReferences()->getTag('0.1');
+
+        $this->assertFalse($tag->isAnnotated(), 'Lightweight tag must not be reported as annotated');
+    }
+
     #[DataProvider('provideFoobar')]
     public function testAnnotatedTag(Repository $repository): void
     {
@@ -94,6 +104,21 @@ public function testAnnotatedTag(Repository $repository): void
         $this->assertEquals('fbde681b329a39e08b63dc54b341a3274c0380c0', $tag->getCommit()->getHash(), 'Tag commit is correct');
     }
 
+    #[DataProvider('provideFoobar')]
+    public function testAnnotatedTagBodyMessageWithBlankLineSeparator(Repository $repository): void
+    {
+        $repository->run('config', ['user.email', 'test@example.com']);
+        $repository->run('config', ['user.name', 'Test']);
+
+        $hash = $repository->getLog()->getSingleCommit()->getHash();
+        $repository->run('tag', ['-a', 'blank-sep', '-m', 'Subject line', '-m', "Body line 1\nBody line 2", $hash]);
+
+        $tag = $repository->getReferences()->getTag('blank-sep');
+
+        $this->assertEquals('Subject line', $tag->getSubjectMessage(), 'Message subject is correct');
+        $this->assertEquals("Body line 1\nBody line 2", $tag->getBodyMessage(), 'Message body has no leading blank line');
+    }
+
     #[DataProvider('provideFoobar')]
     public function testGetTagNotExistingError(Repository $repository): void
     {
diff --git a/tests/Gitonomy/Git/Tests/RepositoryTest.php b/tests/Gitonomy/Git/Tests/RepositoryTest.php
index c0fee88..e7bc480 100644
--- a/tests/Gitonomy/Git/Tests/RepositoryTest.php
+++ b/tests/Gitonomy/Git/Tests/RepositoryTest.php
@@ -13,6 +13,8 @@
 namespace Gitonomy\Git\Tests;
 
 use Gitonomy\Git\Blob;
+use Gitonomy\Git\Commit;
+use Gitonomy\Git\Exception\ReferenceNotFoundException;
 use Gitonomy\Git\Exception\RuntimeException;
 use Gitonomy\Git\Repository;
 use PHPUnit\Framework\Attributes\DataProvider;
@@ -20,6 +22,26 @@
 
 class RepositoryTest extends AbstractTestCase
 {
+    public function testRunReturnsNullInsteadOfThrowingWhenDebugIsFalse(): void
+    {
+        $repository = self::createFoobarRepository(true);
+        $repository = new Repository($repository->getPath(), array_merge(self::getOptions(), ['debug' => false]));
+
+        $this->assertNull($repository->run('not-a-command'));
+    }
+
+    public function testGetShortHashThrowsCleanExceptionWhenDebugIsFalse(): void
+    {
+        $repository = self::createFoobarRepository(true);
+        $repository = new Repository($repository->getPath(), array_merge(self::getOptions(), ['debug' => false]));
+
+        $commit = new Commit($repository, str_repeat('a', 40));
+
+        $this->expectException(ReferenceNotFoundException::class);
+
+        $commit->getShortHash();
+    }
+
     #[DataProvider('provideFoobar')]
     public function testGetBlobWithExistingWorks(Repository $repository): void
     {