def AddEnvironmentVariable(self, environment_variable):
    """Adds an environment variable.

    Args:
      environment_variable (EnvironmentVariableArtifact): environment variable
          artifact.

    Raises:
      KeyError: if the environment variable already exists.
    """
    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
Adds an environment variable.

    Args:
      environment_variable (EnvironmentVariableArtifact): environment variable
          artifact.

    Raises:
      KeyError: if the environment variable already exists.