The process could not be started. : argument "content" is null

I get following Error:

The process could not be started. : argument “content” is null

but why do I get this Error ?
Maybe its because my Rest-Post-Request ?

When can this Error throwing, and how could I solve this issue ?

Can you show the details of the request you’re making and check the Camunda logs for a more detailed error?

This is the Error Message:

  java.lang.NullPointerException: null
    	at com.example.workflow.PostRequestDelegate.post(PostRequestDelegate.java:50) ~[classes/:na]
    	at com.example.workflow.PostRequestDelegate.execute(PostRequestDelegate.java:28) ~[classes/:na]
    	at org.camunda.bpm.engine.impl.bpmn.delegate.JavaDelegateInvocation.invoke(JavaDelegateInvocation.java:40) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.delegate.DelegateInvocation.proceed(DelegateInvocation.java:58) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.delegate.DefaultDelegateInterceptor.handleInvocationInContext(DefaultDelegateInterceptor.java:92) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.delegate.DefaultDelegateInterceptor.handleInvocation(DefaultDelegateInterceptor.java:63) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.bpmn.behavior.ServiceTaskJavaDelegateActivityBehavior.execute(ServiceTaskJavaDelegateActivityBehavior.java:55) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.bpmn.behavior.ServiceTaskJavaDelegateActivityBehavior.performExecution(ServiceTaskJavaDelegateActivityBehavior.java:44) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.bpmn.behavior.TaskActivityBehavior.execute(TaskActivityBehavior.java:69) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.bpmn.behavior.ClassDelegateActivityBehavior$1.call(ClassDelegateActivityBehavior.java:68) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.bpmn.behavior.ClassDelegateActivityBehavior$1.call(ClassDelegateActivityBehavior.java:65) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.bpmn.behavior.AbstractBpmnActivityBehavior.executeWithErrorPropagation(AbstractBpmnActivityBehavior.java:90) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.bpmn.behavior.ClassDelegateActivityBehavior.execute(ClassDelegateActivityBehavior.java:65) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationActivityExecute$2.callback(PvmAtomicOperationActivityExecute.java:61) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationActivityExecute$2.callback(PvmAtomicOperationActivityExecute.java:50) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.PvmExecutionImpl.continueIfExecutionDoesNotAffectNextOperation(PvmExecutionImpl.java:1998) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationActivityExecute.execute(PvmAtomicOperationActivityExecute.java:42) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationActivityExecute.execute(PvmAtomicOperationActivityExecute.java:31) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.AtomicOperationInvocation.execute(AtomicOperationInvocation.java:99) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.invokeNext(CommandInvocationContext.java:131) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performNext(CommandInvocationContext.java:111) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:86) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:645) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:619) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.PvmExecutionImpl$6.callback(PvmExecutionImpl.java:1937) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.PvmExecutionImpl$6.callback(PvmExecutionImpl.java:1934) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.PvmExecutionImpl.continueExecutionIfNotCanceled(PvmExecutionImpl.java:2004) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.PvmExecutionImpl.dispatchDelayedEventsAndPerformOperation(PvmExecutionImpl.java:1953) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.PvmExecutionImpl.dispatchDelayedEventsAndPerformOperation(PvmExecutionImpl.java:1934) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationTransitionNotifyListenerStart.eventNotificationsCompleted(PvmAtomicOperationTransitionNotifyListenerStart.java:60) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationTransitionNotifyListenerStart.eventNotificationsCompleted(PvmAtomicOperationTransitionNotifyListenerStart.java:30) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.core.operation.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:66) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.AtomicOperationInvocation.execute(AtomicOperationInvocation.java:99) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.invokeNext(CommandInvocationContext.java:131) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performNext(CommandInvocationContext.java:111) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:86) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:76) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:654) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:629) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.core.operation.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:62) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.AtomicOperationInvocation.execute(AtomicOperationInvocation.java:99) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.invokeNext(CommandInvocationContext.java:131) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performNext(CommandInvocationContext.java:111) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:86) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:76) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:654) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:629) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.core.operation.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:62) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.AtomicOperationInvocation.execute(AtomicOperationInvocation.java:99) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.invokeNext(CommandInvocationContext.java:131) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performNext(CommandInvocationContext.java:111) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:86) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:76) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:654) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:629) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.core.operation.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:62) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.AtomicOperationInvocation.execute(AtomicOperationInvocation.java:99) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.invokeNext(CommandInvocationContext.java:131) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performNext(CommandInvocationContext.java:111) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:86) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:645) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:619) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationTransitionCreateScope.scopeCreated(PvmAtomicOperationTransitionCreateScope.java:38) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationCreateScope.execute(PvmAtomicOperationCreateScope.java:54) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.pvm.runtime.operation.PvmAtomicOperationCreateScope.execute(PvmAtomicOperationCreateScope.java:28) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.AtomicOperationInvocation.execute(AtomicOperationInvocation.java:99) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.invokeNext(CommandInvocationContext.java:131) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performNext(CommandInvocationContext.java:118) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandInvocationContext.performOperation(CommandInvocationContext.java:86) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:645) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.persistence.entity.ExecutionEntity.startWithFormProperties(ExecutionEntity.java:504) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.cmd.SubmitStartFormCmd.execute(SubmitStartFormCmd.java:85) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.cmd.SubmitStartFormCmd.execute(SubmitStartFormCmd.java:43) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandExecutorImpl.execute(CommandExecutorImpl.java:28) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:110) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:46) ~[camunda-engine-spring-7.13.0.jar:7.13.0]
    	at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:140) ~[spring-tx-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    	at org.camunda.bpm.engine.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:44) ~[camunda-engine-spring-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.ProcessApplicationContextInterceptor.execute(ProcessApplicationContextInterceptor.java:70) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:33) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.impl.FormServiceImpl.submitStartForm(FormServiceImpl.java:79) ~[camunda-engine-7.13.0.jar:7.13.0]
    	at org.camunda.bpm.engine.rest.sub.repository.impl.ProcessDefinitionResourceImpl.submitForm(ProcessDefinitionResourceImpl.java:188) ~[camunda-engine-rest-jaxrs2-7.13.0.jar:7.13.0]
    	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    	at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    	at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.lambda$static$0(ResourceMethodInvocationHandlerFactory.java:52) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:124) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:167) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:219) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:79) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:469) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:391) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:80) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:253) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.internal.Errors$1.call(Errors.java:248) ~[jersey-common-2.29.1.jar:na]
    	at org.glassfish.jersey.internal.Errors$1.call(Errors.java:244) ~[jersey-common-2.29.1.jar:na]
    	at org.glassfish.jersey.internal.Errors.process(Errors.java:292) ~[jersey-common-2.29.1.jar:na]
    	at org.glassfish.jersey.internal.Errors.process(Errors.java:274) ~[jersey-common-2.29.1.jar:na]
    	at org.glassfish.jersey.internal.Errors.process(Errors.java:244) ~[jersey-common-2.29.1.jar:na]
    	at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:265) ~[jersey-common-2.29.1.jar:na]
    	at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:232) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:680) ~[jersey-server-2.29.1.jar:na]
    	at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:392) ~[jersey-container-servlet-core-2.29.1.jar:na]
    	at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:346) ~[jersey-container-servlet-core-2.29.1.jar:na]
    	at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:365) ~[jersey-container-servlet-core-2.29.1.jar:na]
    	at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:318) ~[jersey-container-servlet-core-2.29.1.jar:na]
    	at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:205) ~[jersey-container-servlet-core-2.29.1.jar:na]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.camunda.bpm.webapp.impl.engine.ProcessEnginesFilter.applyFilter(ProcessEnginesFilter.java:144) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.camunda.bpm.webapp.impl.filter.AbstractTemplateFilter.doFilter(AbstractTemplateFilter.java:58) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.camunda.bpm.spring.boot.starter.webapp.filter.LazyDelegateFilter.doFilter(LazyDelegateFilter.java:60) ~[camunda-bpm-spring-boot-starter-webapp-core-7.13.0.jar:7.13.0]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.camunda.bpm.webapp.impl.security.filter.headersec.HttpHeaderSecurityFilter.doFilter(HttpHeaderSecurityFilter.java:87) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.camunda.bpm.spring.boot.starter.webapp.filter.SpringBootCsrfPreventionFilter.doFilter(SpringBootCsrfPreventionFilter.java:136) ~[camunda-bpm-spring-boot-starter-webapp-core-7.13.0.jar:7.13.0]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.camunda.bpm.webapp.impl.security.filter.SecurityFilter.doFilterSecure(SecurityFilter.java:73) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.camunda.bpm.webapp.impl.security.filter.SecurityFilter.doFilter(SecurityFilter.java:57) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.camunda.bpm.spring.boot.starter.webapp.filter.LazyDelegateFilter.doFilter(LazyDelegateFilter.java:60) ~[camunda-bpm-spring-boot-starter-webapp-core-7.13.0.jar:7.13.0]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.camunda.bpm.webapp.impl.security.auth.AuthenticationFilter$1.execute(AuthenticationFilter.java:62) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.camunda.bpm.webapp.impl.security.auth.AuthenticationFilter$1.execute(AuthenticationFilter.java:60) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.camunda.bpm.webapp.impl.security.SecurityActions.runWithAuthentications(SecurityActions.java:44) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.camunda.bpm.webapp.impl.security.auth.AuthenticationFilter.doFilter(AuthenticationFilter.java:60) ~[camunda-webapp-7.13.0-classes.jar:7.13.0]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1639) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
    	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
    	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    	at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

    2020-08-05 13:04:51.334  WARN 18124 --- [nio-8080-exec-1] org.camunda.bpm.engine.rest.exception    : ENGINE-REST-HTTP500 java.lang.NullPointerException
    	at com.example.workflow.PostRequestDelegate.post(PostRequestDelegate.java:50)
    	at com.example.workflow.PostRequestDelegate.execute(PostRequestDelegate.java:28)
    	at org.camunda.bpm.engine.impl.bpmn.delegate.JavaDelegateInvocation.invoke(JavaDelegateInvocation.java:40)
    	at org.camunda.bpm.engine.impl.delegate.DelegateInvocation.proceed(DelegateInvocation.java:58)
    	at org.camunda.bpm.engine.impl.delegate.DefaultDelegateInterceptor.handleInvocationInContext(DefaultDelegateInterceptor.java:92)org.camunda.bpm.webapp.impl.security.filter.headersec.HttpHeaderSecurityFilter.doFilter(HttpHeaderSecurityFilter.java:87)
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    	at org.camunda.bpm.spring.boot.starter.webapp.filter.SpringBootCsrfPreventionFilter.doFilter(SpringBootCsrfPreventionFilter.java:136)
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    	at org.camunda.bpm.webapp.impl.security.filter.SecurityFilter.doFilterSecure(SecurityFilter.java:73)
    	at org.camunda.bpm.webapp.impl.security.filter.SecurityFilter.doFilter(SecurityFilter.java:57)
    	at org.camundajava.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    	at java.base/java.lang.Thread.run(Thread.java:834)

My Post Request is like following:

public void post(){
        MultiValueMap<String, String> parameters = new LinkedMultiValueMap<>();
        headers.setContentType(MediaType.APPLICATION_JSON);
        parameters.add("tcpident","1");
        parameters.add("requestid","2");
        parameters.add("mclass","3");
        parameters.add("mno","4");
        parameters.add("errorstate","5");
        parameters.add("datalength","6");
        parameters.add("resourceid","1");
        parameters.add("ono","2");
        parameters.add("opos","3");
        parameters.add("wpno","23");
        parameters.add("opno","ddsds");
        parameters.add("bufno","d");
        parameters.add("bufpos","ds");
        parameters.add("carrierid","dsdd");
        parameters.add("palletid","dsd");
        parameters.add("palletpos","dsd");
        parameters.add("pno","dsd");
        parameters.add("oposid","ds");
        parameters.add("stepno","dsd");
        parameters.add("maxrecords","dsd");
        parameters.add("boxid","dsd");
        parameters.add("boxpos","dsd");
        parameters.add("mainopos","dsds");
        parameters.add("eltno","dsd");
        parameters.add("cno","dsd");
        parameters.add("boxpno","ds");
        parameters.add("palletpno","dsd");
        parameters.add("aux1int","ds");
        parameters.add("aux2int","ds");
        parameters.add("aux1dint","dsdsd");
        parameters.add("aux2dint","dsd");
        parameters.add("mainpno","dsod");
        HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(parameters);
        ResponseEntity<Call[]> response = restTemplate.postForEntity("http://localhost:8080/calls", request, Call[].class);
    }

I execute post() method in my executeMethode

@Override
public void execute(DelegateExecution delegateExecution) throws Exception {
post();
}

and connecting with my modell Implementation javaClass:
startTCPServersandGetRequest.bpmn (2.2 KB)

Ignore the name of the bpmn file, its just a Post Request.