Get an AJAX error message when user submit an issue via Issue Collector

Steps to reproduce the problem:

1. Add a "Fields Required" validator (from JIRA Suite Utilities add-on) in Create transition and publish the workflow.
2. User will get this error message in UI when they submits an issue via Issue Collector:
   
   In atlassian-jira.log shows this:

   2015-05-28 17:44:19,093 http-bio-8640-exec-12 ERROR admin 1064x1098x1 12e2syf 0:0:0:0:0:0:0:1 /rest/collectors/1.0/template/custom/7f98fd1b [common.error.jersey.ThrowableExceptionMapper] Uncaught exception thrown by REST service: null
   java.lang.NullPointerException
   	at com.atlassian.jira.collector.plugin.rest.TemplateResource.createIssue(TemplateResource.java:457)
   	at com.atlassian.jira.collector.plugin.rest.TemplateResource.createCustomIssue(TemplateResource.java:373)
   	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   	at java.lang.reflect.Method.invoke(Method.java:606)
   	at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)  <+13> (AbstractResourceMethodDispatchProvider.java:205) (ResourceJavaMethodDispatcher.java:75) (HttpMethodRule.java:288) (RightHandPathRule.java:147) (ResourceClassRule.java:108) (RightHandPathRule.java:147) (RootResourceClassesRule.java:84) (WebApplicationImpl.java:1469) (WebApplicationImpl.java:1400) (WebApplicationImpl.java:1349) (WebApplicationImpl.java:1339) (WebComponent.java:416) (ServletContainer.java:537)
   	at com.atlassian.plugins.rest.module.RestDelegatingServletFilter$JerseyOsgiServletContainer.doFilter(RestDelegatingServletFilter.java:178)  <+1> (ServletContainer.java:795)
   	at com.atlassian.plugins.rest.module.RestDelegatingServletFilter.doFilter(RestDelegatingServletFilter.java:73)  <+7> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.jira.tzdetect.IncludeResourcesFilter.doFilter(IncludeResourcesFilter.java:39)  <+3> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.jira.baseurl.IncludeResourcesFilter.doFilter(IncludeResourcesFilter.java:38)  <+13> (AbstractHttpFilter.java:31) (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70) (RestServletUtilsUpdaterFilter.java:26) (RestServletUtilsUpdaterFilter.java:40) (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70) (ContextFilter.java:25) (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.servicedesk.internal.web.RedirectExternalCustomerToPortalFilter.doFilter(RedirectExternalCustomerToPortalFilter.scala:18)  <+4> (AbstractHttpFilter.java:31) (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.mywork.client.filter.ServingRequestsFilter.doFilter(ServingRequestsFilter.java:37)  <+3> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.plugins.cors.CorsFilter.doFilter(CorsFilter.java:65)  <+3> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.prettyurls.filter.PrettyUrlsSiteMeshFixupFilter.doFilter(PrettyUrlsSiteMeshFixupFilter.java:36)  <+3> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.prettyurls.filter.PrettyUrlsDispatcherFilter.doFilter(PrettyUrlsDispatcherFilter.java:60)  <+3> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.prettyurls.filter.PrettyUrlsSiteMeshFilter.doFilter(PrettyUrlsSiteMeshFilter.java:92)  <+3> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.prettyurls.filter.PrettyUrlsMatcherFilter.doFilter(PrettyUrlsMatcherFilter.java:56)  <+3> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.labs.botkiller.BotKillerFilter.doFilter(BotKillerFilter.java:36)  <+18> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (AccessLogFilter.java:103) (AccessLogFilter.java:87) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (XsrfTokenAdditionRequestFilter.java:54) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (ChainedFilterStepRunner.java:87) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (IteratingFilterChain.java:46) (DelegatingPluginFilter.java:70)
   	at com.atlassian.prettyurls.filter.PrettyUrlsCombinedMatchDispatcherFilter.doFilter(PrettyUrlsCombinedMatchDispatcherFilter.java:61)  <+22> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (SecurityFilter.java:239) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (TrustedApplicationsFilter.java:100) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (BaseLoginFilter.java:172) (JiraLoginFilter.java:70) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (IteratingFilterChain.java:46) (DelegatingPluginFilter.java:70) (OAuthFilter.java:79) (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.plugins.rest.module.servlet.RestSeraphFilter.doFilter(RestSeraphFilter.java:40)  <+3> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.prettyurls.filter.PrettyUrlsCombinedMatchDispatcherFilter.doFilter(PrettyUrlsCombinedMatchDispatcherFilter.java:61)  <+9> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (AbstractJohnsonFilter.java:71) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208)
   	at org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:176)
   	at org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:145)
   	at org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:92)  <+10> (UrlRewriteFilter.java:394) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (GzipFilter.java:82) (GzipFilter.java:59) (JiraGzipFilter.java:55) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (IteratingFilterChain.java:46) (DelegatingPluginFilter.java:70)
   	at com.atlassian.analytics.client.filter.JiraAnalyticsFilter.doFilter(JiraAnalyticsFilter.java:41)  <+4> (AbstractHttpFilter.java:31) (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:70)
   	at com.atlassian.prettyurls.filter.PrettyUrlsCombinedMatchDispatcherFilter.doFilter(PrettyUrlsCombinedMatchDispatcherFilter.java:61)  <+40> (DelegatingPluginFilter.java:78) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (ChainedFilterStepRunner.java:87) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (AbstractCachingFilter.java:33) (AbstractHttpFilter.java:31) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (AbstractEncodingFilter.java:41) (AbstractHttpFilter.java:31) (PathMatchingEncodingFilter.java:45) (AbstractHttpFilter.java:31) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (JiraStartupChecklistFilter.java:79) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (MultipartBoundaryCheckFilter.java:41) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (ChainedFilterStepRunner.java:87) (JiraFirstFilter.java:60) (ApplicationFilterChain.java:241) (ApplicationFilterChain.java:208) (StandardWrapperValve.java:220) (StandardContextValve.java:122) (AuthenticatorBase.java:501) (StandardHostValve.java:171) (ErrorReportValve.java:103) (StandardEngineValve.java:116) (AccessLogValve.java:950) (CoyoteAdapter.java:408) (AbstractHttp11Processor.java:1070) (AbstractProtocol.java:611) (JIoEndpoint.java:316)
   	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
   	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
   	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
   	at java.lang.Thread.run(Thread.java:724)
   

Finding:

• Problem happen to a custom script validator which stop user to use the Issue Collector form.

Workaround:

Remove the Fields Required validator