troubleshoot 32bit build

Author: jbrockmendel

pandas/core/groupby/ops.py

@@ -607,7 +607,7 @@ def _call_cython_op(
             # "rank" is the only member of cast_blocklist we get here
             res_dtype = self._get_result_dtype(orig_values.dtype)
             op_result = maybe_downcast_to_dtype(result, res_dtype)
-            if self.how == "first":
+            if self.how == "first" and result_mask is not None and self.uses_mask():
                 # troubleshooting 32bit linux build
                 assert res_dtype == orig_values.dtype, (res_dtype, orig_values.dtype)
                 assert op_result.dtype == res_dtype, (