[STTNHUB-356] fix: Unable to send empty value for UserForm (#1045)

* [STTNHUB-356] fix: Unable to send empty value for UserForm
Was causing the following exception to be raised
```
  File "newsroom/users/forms.py", line 22, in process_formdata
    self.data = [x.strip() for x in valuelist[0].split(",")]
AttributeError: 'NoneType' object has no attribute 'split'
```

* fix formatting

newsroom/users/forms.py

@@ -16,7 +16,9 @@ def _value(self):
             return ""
 
     def process_formdata(self, valuelist):
-        if valuelist == [""]:  # An empty string from the client is equal to an empty array
+        if (
+            valuelist == [""] or valuelist == [None] or valuelist == ["None"]
+        ):  # An empty string from the client is equal to an empty array
             self.data = []
         elif len(valuelist):
             self.data = [x.strip() for x in valuelist[0].split(",")]