code: def get_custom_value(self, key):
          
          self._handled.add(key)
          values = self._lookup[key]
          if len(values) > 1:
              raise RuntimeError(
                  "More than one value for this customParameter: {}".format(key)
              )
          if values:
              return values[0]
          return None
docs: Return the first and only custom parameter matching the given name.