错误内容如下：
angular.js:14199 Error: [ngModel:nonassign] Expression ‘’ is non-assignable. Element:
http://errors.angularjs.org/1.5.11/ngModel/nonassign?p0=&p1=<inputlass%3D"ng-pristine ng-untouched ng-valid" ng-model%3D"">
at http://localhost:3000/bower_components/angular/angular.js:68:12
at NgModelController.$$setOptions (http://localhost:3000/bower_components/angular/angular.js:27915:13)
at Object.ngModelPreLink (http://localhost:3000/bower_components/angular/angular.js:28742:21)
at http://localhost:3000/bower_components/angular/angular.js:1259:18
at invokeLinkFn (http://localhost:3000/bower_components/angular/angular.js:10152:9)
at nodeLinkFn (http://localhost:3000/bower_components/angular/angular.js:9528:11)
at compositeLinkFn (http://localhost:3000/bower_components/angular/angular.js:8810:13)
at compositeLinkFn (http://localhost:3000/bower_components/angular/angular.js:8813:13)
at compositeLinkFn (http://localhost:3000/bower_components/angular/angular.js:8813:13)
at compositeLinkFn (http://localhost:3000/bower_components/angular/angular.js:8813:13)
截图如下：
可以根据提示看出是元素中一个表达没有意义。