Using action=paraminfo on the userrights module:
gives the error "The user parameter must be set", as though action=userrights had been called directly. The query works if a 'user' parameter is given -- any user, so long as they exist:
However, the output of paraminfo is not dependent on this parameter, so it should not be a requirement. No other modules seem to exhibit this behavior; for example
works correctly, even though the edit module has required parameters.