ClassNotFound exception when using 'ResultClass' attribute in Rest Work Item

Issue

When Rest Service task is created, the Result attribute in Output Assignment is set to String by default. When ResultClass is set, then the Result attribute is correctly set to this data type. However, when running process with REST work item configured like this, following exception is observed:

Caused by: java.lang.ClassNotFoundException: com.redhat.demos.hello.CustomModel from [Module "deployment.business-central.war:main" from Service Module Loader]
    at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:213) [jboss-modules.jar:1.3.7.Final-redhat-1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:459) [jboss-modules.jar:1.3.7.Final-redhat-1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:408) [jboss-modules.jar:1.3.7.Final-redhat-1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:389) [jboss-modules.jar:1.3.7.Final-redhat-1]
    at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:134) [jboss-modules.jar:1.3.7.Final-redhat-1]
    at java.lang.Class.forName0(Native Method) [rt.jar:1.7.0_51]
    at java.lang.Class.forName(Class.java:270) [rt.jar:1.7.0_51]
    at org.jbpm.process.workitem.rest.RESTWorkItemHandler.postProcessResult(RESTWorkItemHandler.java:323) [jbpm-workitems-6.3.0.Final-redhat-5.jar:6.3.0.Final-redhat-5]
    ... 82 more