NPE with custom commitHandler with Grid Editor

Originally by Fluffysandals

With the latest 7.6.0 version, grid editor throws a NullPointerException whenever I try to save a bean in a custom CommitHandler.

If I use a custom EditorErrorHandler, I have no other information in the exception other than "Commit failed".
The weird part is that the bean is actually saved in the postCommit() method and there is no other problem detected (all the code in the postCommit() is well executed). The stacktrace is of no help to me :/

This never happened with the same code in Vaadin 7.5.

Stacktace :

com.vaadin.data.fieldgroup.FieldGroup$CommitException: Commit failed
	at com.vaadin.data.fieldgroup.FieldGroup.commit(FieldGroup.java:492)
	at com.vaadin.ui.Grid.saveEditor(Grid.java:6817)
	at com.vaadin.ui.Grid$4.save(Grid.java:4782)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:158)
	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:118)
	at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:408)
	at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:273)
	at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:79)
	at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
	at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1409)
	at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:364)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:180)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	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.core.StandardContextValve.__xr__invoke(StandardContextValve.java)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
	at org.apache.catalina.core.StandardHostValve.__invoke(StandardHostValve.java:170)
	at org.apache.catalina.core.StandardHostValve.__xr__invoke(StandardHostValve.java)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
	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:625)
	at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2522)
	at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2511)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
	at com.vaadin.data.fieldgroup.FieldGroup.commitTransactions(FieldGroup.java:567)
	at com.vaadin.data.fieldgroup.FieldGroup.commit(FieldGroup.java:485)

Imported from https://dev.vaadin.com/ issue #19459

Start at com.vaadin.data.fieldgroup.FieldGroup.commitTransactions, especially FieldGroup.java line 567, then trace the call from FieldGroup.commit through Grid.saveEditor. Reproduce the failure with a custom CommitHandler and EditorErrorHandler using the reported stack trace. Done means saving through the Grid Editor no longer produces the NullPointerException and the regression is covered by a test.