docs: def Parse(self, stat, knowledge_base):
      """Expand any variables in the value."""
      value = stat.registry_data.GetValue()
      if not value:
        raise parser.ParseError("Invalid value for key %s" % stat.pathspec.path)
      value = artifact_utils.ExpandWindowsEnvironmentVariables(
          value, knowledge_base)
      if value:
        yield rdfvalue.RDFString(value)