Use a try-catch to test is uiSrefActive is a valid expression

Author: kmcarpenter

src/stateDirectives.js

@@ -289,14 +289,20 @@ function $StateRefActiveDirective($state, $stateParams, $interpolate) {
   return  {
     restrict: "A",
     controller: ['$scope', '$element', '$attrs', '$timeout', function ($scope, $element, $attrs, $timeout) {
-      var states = [], activeClasses = {}, activeEqClass;
+      var states = [], activeClasses = {}, activeEqClass, uiSrefActive;
 
       // There probably isn't much point in $observing this
       // uiSrefActive and uiSrefActiveEq share the same directive object with some
       // slight difference in logic routing
       activeEqClass = $interpolate($attrs.uiSrefActiveEq || '', false)($scope);
 
-      var uiSrefActive = $scope.$eval($attrs.uiSrefActive) || $interpolate($attrs.uiSrefActive || '', false)($scope);
+      try {
+        uiSrefActive = $scope.$eval($attrs.uiSrefActive);
+      } catch (e) {
+        // Do nothing. uiSrefActive is not a valid expression.
+        // Fall back to using $interpolate below
+      }
+      uiSrefActive = uiSrefActive || $interpolate($attrs.uiSrefActive || '', false)($scope);
       if (isObject(uiSrefActive)) {
         forEach(uiSrefActive, function(stateOrName, activeClass) {
           if (isString(stateOrName)) {