Error launching new process instance - camunda

Question

I have a bpmn process named "vacaciones". I launch correctly inside Java code as follows (this works):
runtimeService.startProcessInstanceByKey("vacaciones");
But using Camunda Rest api the same operation fails. I do the next POST request:
URL-Method POST
http://localhost:7002/rest/engine/default/process-definition/key/vacaciones/start
Headers
Content-Type: application/json
And I get this error response:
GRAVE: Servlet.service() para servlet default lanzó excepción
org.jboss.resteasy.spi.UnhandledException: java.lang.NullPointerException
at org.jboss.resteasy.core.ExceptionHandler.handleApplicationException(ExceptionHandler.java:76)
at org.jboss.resteasy.core.ExceptionHandler.handleException(ExceptionHandler.java:212)
at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:149)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:372)
at org.jboss.resteasy.core.SynchronousDispatcher.invokePropagateNotFound(SynchronousDispatcher.java:217)
at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:224)
at org.jboss.resteasy.plugins.server.servlet.FilterDispatcher.doFilter(FilterDispatcher.java:62)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.camunda.bpm.engine.rest.filter.CacheControlFilter.doFilter(CacheControlFilter.java:41)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:957)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at org.camunda.bpm.engine.rest.sub.repository.impl.ProcessDefinitionResourceImpl.startProcessInstance(ProcessDefinitionResourceImpl.java:95)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:137)
at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:296)
at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:250)
at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:140)
at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:109)
at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:135)
at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:103)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:356)
... 23 more
Whats wrong?

Answer 1

What is your request body? Did you send any? If not I think you have to post an empty JSON object ({}) even if you don't have any variables.

Answer 2

This is the solution. I posted an empty body but if I post the next body it works:
{
"variables": { }
}