NullPointerException when trying to search nonexisting task in Kie Server for BPM Suite 6

Issue

When finding a task by id that does not exists, error 500 is thrown instead of a KieServicesException informing that task does not exists.
Code:

KieServicesConfiguration conf = KieServicesFactory.newRestConfiguration(URL, USER, PASSWORD);
kieServicesClient = KieServicesFactory.newKieServicesClient(conf);
processClient = kieServicesClient.getServicesClient(ProcessServicesClient.class);
userTaskServicesClient = kieServicesClient.getServicesClient(UserTaskServicesClient.class);
queryServicesClient = kieServicesClient.getServicesClient(QueryServicesClient.class);
try {
    userTaskServicesClient.findTaskById(taskId);
}catch (KieServicesException e) {
    // The exception raised here is error 500 instead of 404
}

Instead a 404, we have 500 and a NullPointerException on server side:

ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/kie-server].[org.kie.server.remote.rest.common.KieServerApplication]] (http-127.0.0.1:8180-1) JBWEB000236: Servlet.service() for servlet org.kie.server.remote.rest.common.KieServerApplication threw exception: org.jboss.resteasy.spi.UnhandledException: java.lang.NullPointerException
    at org.jboss.resteasy.core.SynchronousDispatcher.handleApplicationException(SynchronousDispatcher.java:367) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.handleException(SynchronousDispatcher.java:235) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.handleInvokerException(SynchronousDispatcher.java:211) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.getResponse(SynchronousDispatcher.java:576) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:543) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:128) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:208) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:55) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:50) [resteasy-jaxrs-2.3.13.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-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:231) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:512) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169) [jboss-as-web-7.5.7.Final-redhat-3.jar:7.5.7.Final-redhat-3]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:150) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:97) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:854) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:654) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:926) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
    at java.lang.Thread.run(Thread.java:745) [rt.jar:1.8.0_71]
Caused by: java.lang.NullPointerException
    at org.kie.server.services.jbpm.ConvertUtils.convertToTask(ConvertUtils.java:290) [kie-server-services-jbpm-6.5.0.Final-redhat-2.jar:6.5.0.Final-redhat-2]
    at org.kie.server.services.jbpm.RuntimeDataServiceBase.getTaskById(RuntimeDataServiceBase.java:356) [kie-server-services-jbpm-6.5.0.Final-redhat-2.jar:6.5.0.Final-redhat-2]
    at org.kie.server.remote.rest.jbpm.RuntimeDataResource.getTaskById(RuntimeDataResource.java:336) [kie-server-rest-jbpm-6.5.0.Final-redhat-2.jar:6.5.0.Final-redhat-2]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [rt.jar:1.8.0_71]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) [rt.jar:1.8.0_71]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.8.0_71]
    at java.lang.reflect.Method.invoke(Method.java:497) [rt.jar:1.8.0_71]
    at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:168) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invokeOnTarget(ResourceMethod.java:269) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:227) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:216) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.getResponse(SynchronousDispatcher.java:561) [resteasy-jaxrs-2.3.13.Final-redhat-1.jar:]
    ... 20 more

What could be wrong?