Error when passing values for process variable of type HashMap when remotely starting a process in BPM Suite 6

Issue

I am trying to pass a parameter of type java.util.HashMap inside the parameters Map when starting a process remotely and it is failing with the following WARN message in the logs:

WARN  [org.kie.remote.services.cdi.ProcessRequestBean] (mycompanyhost/10.0.0.1:8080-1) Unable to execute StartProcessCommand/0: java.lang.IllegalStateException: Could not unmarshall user-defined class instance parameter of type 'hashMap'
    at org.kie.remote.services.cdi.ProcessRequestBean.verifyObjectHasBeenUnmarshalled(ProcessRequestBean.java:263) [kie-remote-services-6.2.0.Final-redhat-13.jar:6.2.0.Final-redhat-13]
    at org.kie.remote.services.cdi.ProcessRequestBean.checkThatUserDefinedClassesWereUnmarshalled(ProcessRequestBean.java:252) [kie-remote-services-6.2.0.Final-redhat-13.jar:6.2.0.Final-redhat-13]
    at org.kie.remote.services.cdi.ProcessRequestBean.preprocessCommand(ProcessRequestBean.java:227) [kie-remote-services-6.2.0.Final-redhat-13.jar:6.2.0.Final-redhat-13]
    at org.kie.remote.services.cdi.ProcessRequestBean.processCommand(ProcessRequestBean.java:166) [kie-remote-services-6.2.0.Final-redhat-13.jar:6.2.0.Final-redhat-13]
    at org.kie.remote.services.cdi.ProcessRequestBean$Proxy$_$$_WeldClientProxy.processCommand(ProcessRequestBean$Proxy$_$$_WeldClientProxy.java) [kie-remote-services-6.2.0.Final-redhat-13.jar:6.2.0.Final-redhat-13]
    at org.kie.remote.services.rest.ResourceBase.restProcessJaxbCommandsRequest(ResourceBase.java:154) [kie-remote-services-6.2.0.Final-redhat-13.jar:6.2.0.Final-redhat-13]
    at org.kie.remote.services.rest.ExecuteResourceImpl.execute(ExecuteResourceImpl.java:30) [kie-remote-services-6.2.0.Final-redhat-13.jar:6.2.0.Final-redhat-13]
    at org.kie.remote.services.rest.ExecuteResourceImpl$Proxy$_$$_WeldClientProxy.execute(ExecuteResourceImpl$Proxy$_$$_WeldClientProxy.java) [kie-remote-services-6.2.0.Final-redhat-13.jar:6.2.0.Final-redhat-13]

This is working fine in a local JUnit test. What is wrong?