Fix nested_to_record with None values in nested levels (#21164)

Author: ssikdar1

Diff for: doc/source/whatsnew/v0.23.1.txt

@@ -97,6 +97,7 @@ I/O
 
 - Bug in IO methods specifying ``compression='zip'`` which produced uncompressed zip archives (:issue:`17778`, :issue:`21144`)
 - Bug in :meth:`DataFrame.to_stata` which prevented exporting DataFrames to buffers and most file-like objects (:issue:`21041`)
+- Bug when :meth:`pandas.io.json.json_normalize` was called with ``None`` values in nested levels in JSON  (:issue:`21158`)
 - Bug in :meth:`DataFrame.to_csv` and :meth:`Series.to_csv` causes encoding error when compression and encoding are specified (:issue:`21241`, :issue:`21118`)
 - Bug in :meth:`read_stata` and :class:`StataReader` which did not correctly decode utf-8 strings on Python 3 from Stata 14 files (dta version 118) (:issue:`21244`)
 -

Diff for: pandas/io/json/normalize.py

@@ -80,7 +80,7 @@ def nested_to_record(ds, prefix="", sep=".", level=0):
                 if level != 0:  # so we skip copying for top level, common case
                     v = new_d.pop(k)
                     new_d[newkey] = v
-                if v is None:  # pop the key if the value is None
+                elif v is None:  # pop the key if the value is None
                     new_d.pop(k)
                 continue
             else:

Diff for: pandas/tests/io/json/test_normalize.py

@@ -375,3 +375,59 @@ def test_nonetype_dropping(self):
              'info.last_updated': '26/05/2012'}]
 
         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
+        data = {
+            "id": None,
+            "location": {
+                "id": None,
+                "country": {
+                    "id": None,
+                    "state": {
+                        "id": None,
+                        "town.info": {
+                            "region": None,
+                            "x": 49.151580810546875,
+                            "y": -33.148521423339844,
+                            "z": 27.572303771972656}}}
+            }
+        }
+        result = nested_to_record(data)
+        expected = {
+            'location.id': None,
+            'location.country.id': None,
+            'location.country.state.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