Default behaviour for return_type = None corrected.

Added test

bugfix

Final commit

pandas/core/apply.py

@@ -357,7 +357,7 @@ def wrap_results_for_axis(
             # e.g. test_apply_dict GH#8735
             return self.obj._constructor_sliced(results)
         elif self.result_type is None and all(
-            isinstance(x, dict) for x in results.values()
+            isinstance(x, dict) or isinstance(x, tuple) for x in results.values()
         ):
             # Our operation was a to_dict op e.g.
             #  test_apply_dict GH#8735, test_apply_reduce_rows_to_dict GH#25196

pandas/tests/frame/test_apply.py

@@ -97,6 +97,13 @@ def test_apply_empty(self, float_frame):
         result = expected.apply(lambda x: x["a"], axis=1)
         tm.assert_frame_equal(expected, result)
 
+    def test_apply_result_type_None(self):
+        df = DataFrame([['orig1', 'orig2']])
+        expected = Series(data=[('new1', 'new2'), ('new1', 'new2')])
+        result = df.apply(func=lambda col: ('new1', 'new2'))
+        tm.assert_equal(result, expected)
+
+
     def test_apply_with_reduce_empty(self):
         # reduce with an empty DataFrame
         empty_frame = DataFrame()