code: def merge(a, b):
      
      if isinstance(a, CONFIG_VALID) \
              and isinstance(b, CONFIG_VALID):
          # dict update
          if isinstance(a, dict) and isinstance(b, dict):
              a.update(b)
              return a
          # list update
          _a = list(a)
          for x in list(b):
              if x not in _a:
                  _a.append(x)
          return _a
      if a and b:
          raise Exception("Cannot merge")
      raise NotImplementedError
docs: return merged tuples or lists without duplicates
      note: ensure if admin theme is before admin