Code based Odata CLient Proxy Response handler returns Exception when the response contains null

[#1]

hi, 

we are using code based odata client proxy -( rest service ) to send or receive data . i have defined the model class and set the response body structure for the HTTP operation. In the response handler class - /IWBEP/IF_CP_RESPONSE_HANDLER~HANDLE_REST_RESPONSE, it is unable to parse the response to the desired format and getting error /IWBEP/CM_CP-168: Instance of a complex type could not be deserialized. I have defined the response structure fields to be of type string and as nullable. 

Response payload structure: 

[
  {
    "status": 500,
     "id" : null,
    "externalId": null,
"message": "Some string"
  }
]

Some of the fields in the response structure are optional and they are ignored or sent as null by other REST API. Can you please guide what is wrong/missing and how to resolve the error. 

Thanks