<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def GetEnvironmentVariable(self, name):
 """Retrieves an environment variable. Args: name (str):
 name of the environment variable. Returns: EnvironmentVariableArtifact: environment variable artifact or None if there was no value set for the given name. """

    name = name.upper()
    return self._environment_variables.get(name, None)