Add another test case to test id None at diff levels

Author: ssikdar1

pandas/tests/io/json/test_normalize.py

@@ -376,6 +376,33 @@ def test_nonetype_dropping(self):
 
         assert result == expected
 
+    def test_nonetype_top_level_bottom_level(self):
+        # GH21158: If inner level json has a key with a null value
+        # make sure it doesnt do a new_d.pop twice and except
+        data = {
+            "id": None,
+            "location": {
+                "country": {
+                    "state": {
+                        "id": None,
+                        "town.info": {
+                            "id": None,
+                            "region": None,
+                            "x": 49.151580810546875,
+                            "y": -33.148521423339844,
+                            "z": 27.572303771972656}}}
+            }
+        }
+        result = nested_to_record(data)
+        expected = {
+            'location.country.state.id': None,
+            'location.country.state.town.info.id': None,
+            'location.country.state.town.info.region': None,
+            'location.country.state.town.info.x': 49.151580810546875,
+            'location.country.state.town.info.y': -33.148521423339844,
+            'location.country.state.town.info.z': 27.572303771972656}
+        assert result == expected
+
     def test_nonetype_multiple_levels(self):
         # GH21158: If inner level json has a key with a null value
         # make sure it doesnt do a new_d.pop twice and except