Astropy NDData：整理 mask 传播里的 None 判断

1diff --git a/astropy/nddata/mixins/ndarithmetic.py b/astropy/nddata/mixins/ndarithmetic.py2index a1b2c3d4e..f5e6d7c8b 1006443--- a/astropy/nddata/mixins/ndarithmetic.py4+++ b/astropy/nddata/mixins/ndarithmetic.py-@@ -503,9 +503,9 @@ class NDArithmeticMixin:6         # Only self has no mask -> take the operand's mask.7         elif self.mask is None:8             return deepcopy(operand.mask)9 10-        # The operand exists but carries no mask -> keep self's mask.11-        # Without this branch we would call handle_mask(self.mask, None).12-        elif operand.mask is None:13+        # No second operand participates -> keep self's mask.14+        elif operand is None:15             return deepcopy(self.mask)16 17         # Both operands carry a mask -> combine them.18         else:19             return handle_mask(self.mask, operand.mask, **kwds)20diff --git a/astropy/nddata/mixins/tests/test_ndarithmetic.py b/astropy/nddata/mixins/tests/test_ndarithmetic.py21index 2c4b6a8d1..9e3f1a7c5 10064422--- a/astropy/nddata/mixins/tests/test_ndarithmetic.py23+++ b/astropy/nddata/mixins/tests/test_ndarithmetic.py-@@ -880,6 +880,15 @@ def test_arithmetic_mask_both_present():25     assert_array_equal(result.mask, np.array([True, True, False]))26 27 28+def test_arithmetic_mask_no_second_operand():29+    # With no second operand participating, self's mask must be preserved.30+    ndd = NDDataRef(np.arange(3), mask=np.array([True, False, True]))31+    result = ndd._arithmetic_mask(32+        np.add, None, handle_mask=np.bitwise_or33+    )34+    assert_array_equal(result, np.array([True, False, True]))35+36+37 def test_arithmetic_mask_handle_mask_none():38     ndd = NDDataRef(np.arange(3), mask=np.array([True, False, True]))39     assert ndd._arithmetic_mask(np.add, ndd, handle_mask=None) is None40