Merge pull request #19392 from charris/backport-19380

BUG: Fix NULL special case in object-to-any cast code

numpy/core/src/multiarray/dtype_transfer.c

@@ -322,11 +322,11 @@ strided_to_strided_object_to_any(
 
     while (N > 0) {
         memcpy(&src_ref, src, sizeof(src_ref));
-        if (PyArray_Pack(data->descr, dst, src_ref) < 0) {
+        if (PyArray_Pack(data->descr, dst, src_ref ? src_ref : Py_None) < 0) {
             return -1;
         }
 
-        if (data->move_references) {
+        if (data->move_references && src_ref != NULL) {
             Py_DECREF(src_ref);
             memset(src, 0, sizeof(src_ref));
         }

numpy/core/tests/test_casting_unittests.py

@@ -657,3 +657,20 @@ def test_void_and_structured_with_subarray(self, casting):
         expected = casting == "unsafe"
         assert np.can_cast("V4", dtype, casting=casting) == expected
         assert np.can_cast(dtype, "V4", casting=casting) == expected
+
+    @pytest.mark.parametrize("dtype", np.typecodes["All"])
+    def test_object_casts_NULL_None_equivalence(self, dtype):
+        # None to <other> casts may succeed or fail, but a NULL'ed array must
+        # behave the same as one filled with None's.
+        arr_normal = np.array([None] * 5)
+        arr_NULLs = np.empty_like([None] * 5)
+        # If the check fails (maybe it should) the test would lose its purpose:
+        assert arr_NULLs.tobytes() == b"\x00" * arr_NULLs.nbytes
+
+        try:
+            expected = arr_normal.astype(dtype)
+        except TypeError:
+            with pytest.raises(TypeError):
+                arr_NULLs.astype(dtype)
+        else:
+            assert_array_equal(expected, arr_NULLs.astype(dtype))