NullPointerException when sending JSON commands to Decision Server in JBoss BRMS 6.2

Issue

I am trying to send a request of type JSON to a BRMS 6.2 Decision Server container and the response is a NullPointerException error:

{
  "type" : "FAILURE",
  "msg" : "Error calling container test: java.lang.NullPointerException: null",
  "result" : null
}

In the server logs I can see an error:

Error calling container 'test': java.lang.NullPointerException
    at org.drools.core.command.runtime.BatchExecutionCommandImpl.execute(BatchExecutionCommandImpl.java:135) [drools-core-6.3.0.Final-redhat-5.jar:6.3.0.Final-redhat-5]
    at org.drools.core.command.runtime.BatchExecutionCommandImpl.execute(BatchExecutionCommandImpl.java:51) [drools-core-6.3.0.Final-redhat-5.jar:6.3.0.Final-redhat-5]
    at org.drools.core.impl.StatefulKnowledgeSessionImpl.execute(StatefulKnowledgeSessionImpl.java:738) [drools-core-6.3.0.Final-redhat-5.jar:6.3.0.Final-redhat-5]
    at org.drools.core.impl.StatefulKnowledgeSessionImpl.execute(StatefulKnowledgeSessionImpl.java:712) [drools-core-6.3.0.Final-redhat-5.jar:6.3.0.Final-redhat-5]
    at org.kie.server.services.impl.KieContainerCommandServiceImpl.callContainer(KieContainerCommandServiceImpl.java:103) [kie-server-services-common-6.3.0.Final-redhat-5.jar:6.3.0.Final-redhat-5]
    at org.kie.server.remote.rest.drools.CommandResource.manageContainer(CommandResource.java:73) [kie-server-rest-drools-6.3.0.Final-redhat-5.jar:6.3.0.Final-redhat-5]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [rt.jar:1.7.0_60]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) [rt.jar:1.7.0_60]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.7.0_60]
    at java.lang.reflect.Method.invoke(Method.java:606) [rt.jar:1.7.0_60]
    at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:168) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invokeOnTarget(ResourceMethod.java:269) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:227) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:216) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.getResponse(SynchronousDispatcher.java:561) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:543) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:128) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:208) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:55) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:50) [resteasy-jaxrs-2.3.12.Final-redhat-1.jar:]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-2.jar:1.0.2.Final-redhat-2]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:295) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:231) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:512) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169) [jboss-as-web-7.5.4.Final-redhat-4.jar:7.5.4.Final-redhat-4]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:150) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:97) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:400) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:854) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:653) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:926) [jbossweb-7.5.11.Final-redhat-1.jar:7.5.11.Final-redhat-1]
    at java.lang.Thread.run(Thread.java:745) [rt.jar:1.7.0_60]

This is what my JSON looks like:

{"batch-execution":{"commands":{"fire-all-rules":""}}}

What could be wrong?