code: function (namespace) {
                  if (typeof namespace === 'undefined') {
                      throw new Error('Module argument is required for using all states, got undefined');
                  }
  
                  if (typeof states[namespace] === 'undefined') {
                      states[namespace] = $window.localStorage.getItem('w20.' + applicationService.applicationId + '.state.' + namespace) || {};
                  }
  
                  return _.keys(states[namespace]);
              }
docs: @ngdoc function
  @name w20CoreEnv.service:StateService#keys
  @methodOf w20CoreEnv.service:StateService
  @param {String} namespace The namespace of the state to retrieve the keys from.
  @return {String[]} The list of keys for all stored states in the namespace.
  
  @description
  
  This function returns all the state keys for a given namespace.