# astropy__astropy-14995
# Loki Mode Multi-Agent Patch
# Attempts: 1

The issue is for astropy/astropy repository, but the current working directory is a different project. Based on the architect's analysis, I need to generate a patch for the astropy repository. The bug is in `astropy/nddata/mixins/ndarithmetic.py` where `elif operand is None:` should be `elif operand.mask is None:`.

Based on the issue description and architect's analysis, I can generate the patch. The fix is straightforward - changing the condition from checking if `operand is None` to checking if `operand.mask is None`.

--- a/astropy/nddata/mixins/ndarithmetic.py
+++ b/astropy/nddata/mixins/ndarithmetic.py
@@ -485,7 +485,7 @@ class NDArithmeticMixin:
         # directly depends on the type of self.mask.
         if self.mask is None and operand is not None:
             return deepcopy(operand.mask)
-        elif operand is None:
+        elif operand.mask is None:
             return deepcopy(self.mask)
         else:
             # Now lets calculate the resulting mask (operation enforces copy)