fix: tolerate data-less HDUs in the database scrape

autofit/database/model/array.py

@@ -169,14 +169,22 @@ def header(self):
     def header(self, header):
         self._header = header.tostring()
 
+    @property
+    def has_data(self):
+        """
+        Whether this HDU carries an array payload. A data-less HDU stores no
+        shape, which is how it is distinguished from one holding an array.
+        """
+        return self._shape is not None
+
     @property
     def hdu(self):
         from astropy.io import fits
 
         type_ = fits.PrimaryHDU if self.is_primary else fits.ImageHDU
 
         return type_(
-            self.array,
+            self.array if self.has_data else None,
             self.header,
         )
 
@@ -185,7 +193,18 @@ def hdu(self, hdu):
         from astropy.io import fits
 
         self.is_primary = isinstance(hdu, fits.PrimaryHDU)
-        self.array = hdu.data
+
+        # A data-less HDU is legitimate and routine: the first HDU of a
+        # multi-extension FITS is conventionally an empty PrimaryHDU, and
+        # `AggregateFITS` emits exactly that. Leave the array columns null
+        # rather than dereferencing `hdu.data.dtype` on None.
+        if hdu.data is None:
+            self._dtype = None
+            self._shape = None
+            self.bytes = None
+        else:
+            self.array = hdu.data
+
         self.header = hdu.header
 
     @property

test_autofit/database/test_file_types.py

@@ -54,3 +54,34 @@ def test_hdu(hdu, hdu_array):
     loaded = db_hdu.hdu
     assert (loaded.data == hdu_array).all()
     assert loaded.header == hdu.header
+
+
+def test_hdu_without_data():
+    """
+    A data-less HDU must round-trip. The first HDU of a multi-extension FITS is
+    conventionally an empty `PrimaryHDU` — `AggregateFITS` emits exactly that —
+    so dereferencing `hdu.data.dtype` here broke every such scrape.
+    """
+    db_hdu = db.HDU(name="test", hdu=fits.PrimaryHDU())
+
+    assert not db_hdu.has_data
+
+    loaded = db_hdu.hdu
+    assert isinstance(loaded, fits.PrimaryHDU)
+    assert loaded.data is None
+
+
+def test_set_fits_with_empty_primary_hdu(fit, hdu_array):
+    """
+    The shape the database scrape actually meets: an empty `PrimaryHDU`
+    followed by named image extensions.
+    """
+    image_hdu = fits.ImageHDU(hdu_array)
+    image_hdu.header["EXTNAME"] = "MODEL_IMAGE"
+
+    fit.set_fits("test", fits.HDUList([fits.PrimaryHDU(), image_hdu]))
+
+    loaded = fit.get_fits("test")
+    assert len(loaded) == 2
+    assert loaded[0].data is None
+    assert (loaded[1].data == hdu_array).all()