code: def AddEnvironmentVariable(self, environment_variable):
      
      name = environment_variable.name.upper()
      if name in self._environment_variables:
        raise KeyError('Environment variable: {0:s} already exists.'.format(
            environment_variable.name))
  
      self._environment_variables[name] = environment_variable
docs: Adds an environment variable.
  
      Args:
        environment_variable (EnvironmentVariableArtifact): environment variable
            artifact.
  
      Raises:
        KeyError: if the environment variable already exists.