angularjs - Firebase: Error: Key content was undefined. Cannot pass undefined in JSON. Use null instead." -

trying firebase first time. got whole thing working in plunkr here: http://plnkr.co/3wirbn

var app = angular.module('myapp',['firebase']);  app.factory('chatmessages',["$firebasearray",function($firebasearray){ var ref = new firebase('https://scanapp.firebaseio.com/tut');     return $firebasearray(ref); }]);   app.controller('mycontroller'['$scope','chatmessages',function($scope,chatmessages){  $scope.test = 'hello world'; $scope.user = "anonymouse"; $scope.messages = chatmessages;  $scope.addmessage = function(){     $scope.messages.$add({         from: $scope.user,         content: $scope.message     });     $scope.message = ''; };   }]); 

i tried following tutorials on site, did quick start stuff read docs thoroughly, keep getting error above:

"error: key content undefined. cannot pass undefined in json. use null instead."

i can working in above plunk, understand concepts. copied same code plunk, , cdn links project, same error. im using ionic framework web-based app. angular , still working fine,i error when trying hit "add" button run function.

update: has inputs. if set "from" , "content" key , field strings rather bound $scope, works:

    $scope.addmessage = function(){     $scope.messages.$add({         from: 'test',         content: 'stuff'     });     $scope.message = ''; }; 

but isn't useful other sending same data on , on again.

you have $scope.messages in form. form creates new scope. remove form , replace button following:<button ng-click="addmessage()">add</button> doesn't create new scope , message added firebase. @ least worked me.