Modify code to get projection matrix

Hi,
I want to write an interface for the projection matrix of camera, and follow the code modification of this issue: https://github.com/allenai/ai2thor/issues/110.
However, when I run the local build version, it always stuck at "controller.start()". The log shows the following error:

JsonSerializationException: Self referencing loop detected for property 'normalized' with type 'UnityEngine.Quaternion'. Path 'agents[0].objects[0].projectionMatrix.rotation'.
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference

I follow this link: https://stackoverflow.com/questions/7397207/json-net-error-self-referencing-loop-detected-for-type, trying to solve this problem, but it does not work. To be more precise, I tried to modify the JsonConvert setting to " PreserveReferencesHandling = PreserveReferencesHandling.Objects". I also tried to add "[JsonObject(IsReference = true)] " to "objectMetadata" class, but it doesn't work either. I just want to know how I can get this modification work?