1>created a user with all privilages
2>created a process model and attached a form to it
3>created an app and attached it with process model and published it
4>on start process tab when we select the created process and hit start button nothing happens and following error appear on console
can you please let me know the reason for this error
2019-01-09 12:13:59.996 INFO 25656 — [nio-8080-exec-5] o.s.w.s.DispatcherServlet : FrameworkServlet ‘dispatcherServlet’: initialization started
2019-01-09 12:14:00.060 INFO 25656 — [nio-8080-exec-5] o.s.w.s.DispatcherServlet : FrameworkServlet ‘dispatcherServlet’: initialization completed in 63 ms
2019-01-09 12:14:25.275 ERROR 25656 — [nio-8080-exec-8] o.s.b.w.s.s.ErrorPageFilter : Forwarding to error page from request [/app/rest/process-instances] due to exception [null]
java.lang.NullPointerException: null
at java.util.HashMap.putMapEntries(HashMap.java:500) ~[?:1.8.0_31]
at java.util.HashMap.putAll(HashMap.java:784) ~[?:1.8.0_31]
at org.flowable.engine.impl.runtime.ProcessInstanceBuilderImpl.startFormVariables(ProcessInstanceBuilderImpl.java:151) ~[flowable-engine-6.4.1-SNAPSHOT.jar:6.4.1-SNAPSHOT]
at org.flowable.engine.impl.RuntimeServiceImpl.startProcessInstanceWithForm(RuntimeServiceImpl.java:170) ~[flowable-engine-6.4.1-SNAPSHOT.jar:6.4.1-SNAPSHOT]
at org.flowable.ui.task.service.runtime.FlowableProcessInstanceService.startNewProcessInstance(FlowableProcessInstanceService.java:132) ~[flowable-ui-task-logic-6.4.1-SNAPSHOT.jar:6.4.1-SNAPSHOT]
at org.flowable.ui.task.service.runtime.FlowableProcessInstanceService$$FastClassBySpringCGLIB$$6558533.invoke() ~[flowable-ui-task-logic-6.4.1-SNAPSHOT.jar:6.4.1-SNAPSHOT]
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) ~[spring-core-5.0.11.RELEASE.jar:5.0.11.RELEASE]
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:746) ~[spring-aop-5.0.11.RELEASE.jar:5.0.11.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.0.11.RELEASE.jar:5.0.11.RELEASE]
at org.springframework.transaction.interceptor.TransactionInterceptor$$Lambda$2577/2062547351.proceedWithInvocation(Unknown Source) ~[?:?]
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:294) ~[spring-tx-5.0.11.RELEASE.jar:5.0.11.RELEASE]
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98) ~[spring-tx-5.0.11.RELEASE.jar:5.0.11.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.11.RELEASE.jar:5.0.11.RELEASE]
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688) ~[spring-aop-5.0.11.RELEASE.jar:5.0.11.RELEASE]
at org.flowable.ui.task.service.runtime.FlowableProcessInstanceService$$EnhancerBySpringCGLIB$$bec2d338.startNewProcessInstance() ~[flowable-ui-task-logic-6.4.1-SNAPSHOT.jar:6.4.1-SNAPSHOT]