@staticmethod<EOL><INDENT>def _get_env_vars_value(filename):<DEDENT>
if not filename:<EOL><INDENT>return None<EOL><DEDENT>try:<EOL><INDENT>with open(filename, '<STR_LIT:r>') as fp:<EOL><INDENT>return json.load(fp)<EOL><DEDENT><DEDENT>except Exception as ex:<EOL><INDENT>raise InvokeContextException("<STR_LIT>".format(<EOL>filename,<EOL>str(ex)))<EOL><DEDENT>
If the user provided a file containing values of environment variables, this method will read the file and
return its value

:param string filename: Path to file containing environment variable values
:return dict: Value of environment variables, if provided. None otherwise
:raises InvokeContextException: If the file was not found or not a valid JSON