BUG: test that no error is raised on df.where() with empty df & cond

pandas/tests/frame/test_indexing.py

@@ -2939,6 +2939,15 @@ def test_where_callable(self):
         tm.assert_frame_equal(result,
                               (df + 2).where((df + 2) > 8, (df + 2) + 10))
 
+    def test_where_empty_df_and_empty_cond_having_non_bool_dtypes(self):
+        # GH 21947
+        data = []
+        df = pd.DataFrame(columns=['a'], data=data)
+        cond = df.applymap(lambda x: x > 0)
+        # Should not raise ValueError:
+        # Boolean array expected for the condition, not object
+        df.where(cond)
+
     def test_where_tz_values(self, tz_naive_fixture):
         df1 = DataFrame(DatetimeIndex(['20150101', '20150102', '20150103'],
                                       tz=tz_naive_fixture),