fix: Fix Null index assign series to column (#711)

Author: TrevorBergeron

bigframes/dataframe.py

@@ -400,11 +400,12 @@ def memory_usage(self, index: bool = True):
         column_sizes = self.dtypes.map(
             lambda dtype: bigframes.dtypes.DTYPE_BYTE_SIZES.get(dtype, 8) * n_rows
         )
-        if index:
+        if index and self._has_index:
             index_size = pandas.Series([self.index._memory_usage()], index=["Index"])
             column_sizes = pandas.concat([index_size, column_sizes])
         return column_sizes
 
+    @requires_index
     def info(
         self,
         verbose: Optional[bool] = None,
@@ -768,7 +769,7 @@ def _apply_series_binop_axis_0(
             block = block.drop_columns([get_column_left[column_id]])
 
         block = block.drop_columns([series_col])
-        block = block.with_index_labels(self.index.names)
+        block = block.with_index_labels(self._block.index.names)
         return DataFrame(block)
 
     def _apply_series_binop_axis_1(
@@ -1611,7 +1612,7 @@ def _assign_series_join_on_index(
             # Update case, remove after copying into columns
             block = block.drop_columns([source_column])
 
-        return DataFrame(block.with_index_labels(self.index.names))
+        return DataFrame(block.with_index_labels(self._block.index.names))
 
     def reset_index(self, *, drop: bool = False) -> DataFrame:
         block = self._block.reset_index(drop)
@@ -3283,7 +3284,7 @@ def _prepare_export(
         array_value = self._block.expr
 
         new_col_labels, new_idx_labels = utils.get_standardized_ids(
-            self._block.column_labels, self.index.names
+            self._block.column_labels, self._block.index.names
         )
 
         columns = list(self._block.value_columns)
@@ -3320,7 +3321,7 @@ def _run_io_query(
         session = self._block.expr.session
         self._optimize_query_complexity()
         export_array, id_overrides = self._prepare_export(
-            index=index, ordering_id=ordering_id
+            index=index and self._has_index, ordering_id=ordering_id
         )
 
         _, query_job = session._execute(

tests/system/small/test_empty_index.py

@@ -169,6 +169,21 @@ def test_empty_index_df_self_aligns(
     )
 
 
+def test_empty_index_setitem(scalars_df_empty_index, scalars_pandas_df_default_index):
+    bf_result = scalars_df_empty_index.copy()
+    bf_result["new_col"] = (
+        scalars_df_empty_index["int64_col"] + scalars_df_empty_index["float64_col"]
+    )
+    pd_result = scalars_pandas_df_default_index.copy()
+    pd_result["new_col"] = (
+        scalars_pandas_df_default_index["int64_col"]
+        + scalars_pandas_df_default_index["float64_col"]
+    )
+    pd.testing.assert_frame_equal(
+        bf_result.to_pandas(), pd_result.reset_index(drop=True), check_dtype=False
+    )
+
+
 def test_empty_index_df_concat(scalars_df_empty_index, scalars_pandas_df_default_index):
     bf_result = bpd.concat([scalars_df_empty_index, scalars_df_empty_index])
     pd_result = pd.concat(