Hello, I'm getting the following exception which I can't seem to find reference to anywhere on Google. Its happening in TreeDataService.ashx when trying to retrieve and display a custom tree that was working fine in the previous Umbraco version. Is anyone familiar with this?

[NullReferenceException: Object reference not set to an instance of an object.]
umbraco.cms.presentation.Trees.JsTreeNodeConverter.Serialize(Object obj, JavaScriptSerializer serializer) +312
System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember) +85
System.Web.Script.Serialization.JavaScriptSerializer.SerializeEnumerable(IEnumerable enumerable, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat) +127
System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember) +1306
System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember) +197
System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, StringBuilder output, SerializationFormat serializationFormat) +28
System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, SerializationFormat serializationFormat) +66
System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj) +6
umbraco.businesslogic.Utils.JSONSerializer.Serialize(Object obj) +76
umbraco.cms.presentation.Trees.XmlTree.ToString(SerializedTreeType type) +170
umbraco.cms.presentation.Trees.XmlTree.ToString() +61
umbraco.presentation.webservices.TreeDataService.ProcessRequest(HttpContext context) +120
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +341
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69