Null Pointer Exception trying to modify process variable value from Rule

Create a simple process flow with the following nodes: 1. start 2. script task that contain this script kcontext.getKnowledgeRuntime().insert(kcontext.getProcessInstance()); 3. business rule task that execute the following rule flow group import org.drools.runtime.process.WorkflowProcessInstance rule AlterName ruleflow-group "ProcessName" when processInstance : WorkflowProcessInstance() eval(1 < 18); then processInstance.setVariable("name", "NewName"); end 4. add any other task nodes after that, can be human task, script task, whatever. 5. end task 6. generate the task forms. 7. start the process from jbpm-console 8. get null pointer exception