docs: def deep_merge(base, extra):
      """
      Deeply merge two dictionaries, overriding existing keys in the base.
  
      :param base: The base dictionary which will be merged into.
      :param extra: The dictionary to merge into the base. Keys from this
          dictionary will take precedence.
      """
      if extra is None:
          return
  
      for key, value in extra.items():
          if value is None:
              if key in base:
                  del base[key]
          # If the key represents a dict on both given dicts, merge the sub-dicts
          elif isinstance(base.get(key), dict) and isinstance(value, dict):
              deep_merge(base[key], value)
          else:
              # Otherwise, set the key on the base to be the value of the extra.
              base[key] = value