def MapOf(self, variable, type_name):
    if self.map_of_policy:
      return self.ApplyFormat(variable, type_name, self.map_of_policy)
    # COV_NF_START
    raise NotImplementedError(
        'Subclasses of LanguageModel must implement MapOf or provide'
        ' map_of_policy')
    # COV_NF_END
Produce the string declaring a map of string to a data type.
dataset/ETHPy150Open google/apis-client-generator/src/googleapis/codegen/language_model.py/LanguageModel.MapOf