Error in updating values from Java Client

I have written Java client subclassing VirtualThing similar to SteamThing and SteamSensorClient. I am updating five different values. Only three of them getting updated. I am seeing the following error in the client console. Any help will be greatly appreciated.

Thanks in advance.

09:49:38.755 DEBUG c.t.c.c.e.m.CommunicationEndpointMonitorTask - CommunicationEndpoint Monitor - checking for disconnected endpoints

DE001 - Position: 0.8559873665751253

DE001 - Speed: 28

DE001 - CurrentFuelTemperature: 24

DE001 - MAP Voltage: 1.7187178145076012

DE001 - Oxygen Voltage: 0.04258031328471801

09:49:38.920 DEBUG c.t.c.c.e.CommunicationEndpoint - Sending synchronous message, waiting for response [sync key: 44, message: APIRequestMessage requestId: 44, endpointId: 0, sessionId: 6, method: POST, entityName: *DE001, characteristic: Services, target: UpdateSubscribedPropertyValues]

09:49:38.921 DEBUG i.n.h.c.h.w.WebSocket08FrameEncoder - Encoding WebSocket Frame opCode=2 length=361

09:49:38.924 DEBUG i.n.h.c.h.w.WebSocket08FrameDecoder - Decoding WebSocket Frame opCode=2

09:49:38.924 DEBUG i.n.h.c.h.w.WebSocket08FrameDecoder - Decoding WebSocket Frame length=187

09:49:38.925 DEBUG c.t.c.c.e.DispatchingClientEndpoint - RESPONSE received endpoint id: 0, duration: 4 ResponseMessage requestId: 44, endpointId: 0, sessionId: -1, code: STATUS_SUCCESS, multipart: false, packet #: 0, total packets: 0

09:49:38.925 ERROR c.t.c.client.things.VirtualThing - Unable To Update Subscribed Properties For DieselEngine001 : Unable to dispatch : Unable to Invoke Service UpdateSubscribedPropertyValues on DieselEngine001 : null</p></font>