push fillna into op

Author: TrevorBergeron

bigframes/core/compile/ibis_compiler/scalar_op_registry.py

@@ -1062,7 +1062,7 @@ def isin_op_impl(x: ibis_types.Value, op: ops.IsInOp):
     if op.match_nulls and contains_nulls:
         return x.isnull() | x.isin(matchable_ibis_values)
     else:
-        return x.isin(matchable_ibis_values)
+        return x.isin(matchable_ibis_values).fillna(False)
 
 
 @scalar_op_compiler.register_unary_op(ops.ToDatetimeOp, pass_op=True)

bigframes/dataframe.py

@@ -2755,11 +2755,11 @@ def isin(self, values) -> DataFrame:
                         False, label=label, dtype=pandas.BooleanDtype()
                     )
                     result_ids.append(result_id)
-            return DataFrame(block.select_columns(result_ids)).fillna(value=False)
+            return DataFrame(block.select_columns(result_ids))
         elif utils.is_list_like(values):
             return self._apply_unary_op(
                 ops.IsInOp(values=tuple(values), match_nulls=True)
-            ).fillna(value=False)
+            )
         else:
             raise TypeError(
                 "only list-like objects are allowed to be passed to "