Fix a bug in NDData constructor where WCS was not validated correctly

astropy/nddata/ccddata.py

@@ -224,7 +224,7 @@ def wcs(self):
 
     @wcs.setter
     def wcs(self, value):
-        if not isinstance(value, WCS):
+        if value is not None and not isinstance(value, WCS):
             raise TypeError("the wcs must be a WCS instance.")
         self._wcs = value
 

astropy/nddata/nddata.py

@@ -227,7 +227,8 @@ def __init__(self, data, uncertainty=None, mask=None, wcs=None,
         # Store the attributes
         self._data = data
         self.mask = mask
-        self._wcs = wcs
+        self._wcs = None
+        self.wcs = wcs
         self.meta = meta  # TODO: Make this call the setter sometime
         self._unit = unit
         # Call the setter for uncertainty to further check the uncertainty

astropy/nddata/tests/test_nddata.py

@@ -518,3 +518,10 @@ def test_nddata_wcs_setter_with_low_level_wcs():
     ndd.wcs = low_level
 
     assert isinstance(ndd.wcs, BaseHighLevelWCS)
+
+
+def test_nddata_init_with_low_level_wcs():
+    wcs = WCS()
+    low_level = SlicedLowLevelWCS(wcs, 5)
+    ndd = NDData(np.ones((5, 5)), wcs=low_level)
+    assert isinstance(ndd.wcs, BaseHighLevelWCS)

docs/changes/nddata/11985.bugfix.rst

@@ -0,0 +1,2 @@
+Ensure that the ``wcs=`` argument to ``NDData`` is always parsed into a high
+level WCS object.