title: UI-router throw error as `Invalid state ref`, when adding link to `ui-sref'
body: <p>for the following <code>route</code> :</p>
  
  <pre><code>.state('user', {
                  url:'/user/:userId',
                  templateUrl : 'app/views/pages/user/user.html',
                  controller  : 'userController as user',
                  required    : true,
                  resolve     : {
                      userData : function( $q, api, $stateParams ){
  
                          console.log('hi', $stateParams)
  
                          var differed = $q.defer();
  
                          api.getUsers().then(function( data ){
                              differed.resolve( data.data );
                          });
  
                          return differed.promise;
  
                      }
                  }
              })
  </code></pre>
  
  <p>I am calling from one of my html as like this:</p>
  
  <pre><code>&lt;li ng-repeat="user in users.usersData"&gt;&lt;a ui-sref="user(userId:{user._id})"&gt;{{user.name}}&lt;/a&gt;&lt;/li&gt;
  </code></pre>
  
  <p>But getting error as :</p>
  
  <pre><code>angular.js:13920 Error: [$parse:syntax] 
  
  https://docs.angularjs.org/error/$parse/syntax?p0=:&amp;p1=is%20an%20unexpected%20token&amp;p2=7&amp;p3=userId:%7Buser._id%7D&amp;p4=:%7Buser._id%7D
  </code></pre>
  
  <p>what is wrong with my code? any one help me here?</p>