'Expand any variables in the value.'

def Parse(self, stat, knowledge_base):

    value = stat.registry_data.GetValue()
    if (not value):
        raise parsers.ParseError(('Invalid    value    for    key    %s' % stat.pathspec.path))
    value = artifact_utils.ExpandWindowsEnvironmentVariables(value, knowledge_base)
    if value:
        (yield rdfvalue.RDFString(value))
