[Python] Python recursive dict code is dropping key, values where the value is None

I am trying to loop over all elements in a json file. I load into a python dict object and then I am "walking" over it with recursion. The issue is when I have a chunks like this:

{
"layerId": "xxxx",
"url": "https://xxxx.com/server/rest/services/General/Boundaries/MapServer/2",
"name": "Grid",
"placeholder": "",
"searchFields": [
"GRID"
],
"displayField": "GRID",
"exactMatch": false,
"searchInCurrentMapExtent": false,
"panToScale": false,
"zoomScale": null,
"maxSuggestions": 6,
"maxResults": 6,
"type": "query"
}


The code is dropping the '"zoomScale": null' key-value in the output.

def update_json(data, url_target, item_type, source_id=None, target_id=None):
def recursive_update(data):
if isinstance(data, dict):
return {k: recursive_update(v) for k, v in data.items()}
elif isinstance(data, list):
return [recursive_update(x) for x in data]
elif isinstance(data, str):
temp = data.replace('xxxx.com', url_target)
if item_type == 'app':
temp = temp.replace(source_id, target_id)
return temp
elif data is None:
return None
else:
return data
return recursive_update(data)


If I change the return value to something other than None when data is None, e.g. 'test_null' then the key-value, 'zoomScale":"test_null"', is retained. Why is it dropping the key-value when the value is None and how can I keep the key-value in the dictionary?

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