Gitlab Webhooks pipeline event returns sourceProjectId must not be null

## Issue

### Context
- **Gitlab plugin version**: 1.5.12
- **Gitlab version**: 11.11.3-ee
- **Jenkins version**: 2.164.3
- **Job type**: Pipeline.

### Logs & Traces

java.lang.NullPointerException: sourceProjectId must not be null.
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:204)
at com.dabsquared.gitlabjenkins.cause.CauseData.<init>(CauseData.java:74)
at com.dabsquared.gitlabjenkins.cause.CauseDataBuilder.build(CauseDataBuilder.java:632)
at com.dabsquared.gitlabjenkins.trigger.handler.pipeline.PipelineHookTriggerHandlerImpl.retrieveCauseData(PipelineHookTriggerHandlerImpl.java:128)
at com.dabsquared.gitlabjenkins.trigger.handler.pipeline.PipelineHookTriggerHandlerImpl.retrieveCauseData(PipelineHookTriggerHandlerImpl.java:32)
at com.dabsquared.gitlabjenkins.trigger.handler.AbstractWebHookTriggerHandler.createActions(AbstractWebHookTriggerHandler.java:85)
at com.dabsquared.gitlabjenkins.trigger.handler.pipeline.PipelineHookTriggerHandlerImpl.handle(PipelineHookTriggerHandlerImpl.java:70)
at com.dabsquared.gitlabjenkins.trigger.handler.pipeline.PipelineHookTriggerHandlerImpl.handle(PipelineHookTriggerHandlerImpl.java:32)
at com.dabsquared.gitlabjenkins.GitLabPushTrigger.onPost(GitLabPushTrigger.java:481)
at com.dabsquared.gitlabjenkins.webhook.build.PipelineBuildAction$1.performOnPost(PipelineBuildAction.java:76)
at com.dabsquared.gitlabjenkins.webhook.build.BuildWebHookAction$TriggerNotifier.run(BuildWebHookAction.java:54)
at hudson.security.ACL.impersonate(ACL.java:273)
at com.dabsquared.gitlabjenkins.webhook.build.PipelineBuildAction.execute(PipelineBuildAction.java:73)
at com.dabsquared.gitlabjenkins.webhook.build.BuildWebHookAction.execute(BuildWebHookAction.java:31)
at com.dabsquared.gitlabjenkins.webhook.GitLabWebHook.getDynamic(GitLabWebHook.java:44)
at java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:627)
at org.kohsuke.stapler.Function$MethodFunction.invoke(Function.java:396)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:408)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:212)
at org.kohsuke.stapler.MetaClass$9.dispatch(MetaClass.java:456)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:739)
Caused: javax.servlet.ServletException
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:789)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:870)
at org.kohsuke.stapler.MetaClass$9.dispatch(MetaClass.java:458)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:739)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:870)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:668)
at org.kohsuke.stapler.Stapler.service(Stapler.java:238)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:865)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1655)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:154)
at jenkins.telemetry.impl.UserLanguages$AcceptLanguageFilter.doFilter(UserLanguages.java:128)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:151)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:157)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
at com.dabsquared.gitlabjenkins.webhook.GitLabWebHook$GitlabWebHookCrumbExclusion.process(GitLabWebHook.java:53)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:73)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:117)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:135)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.BasicHeaderProcessor.doFilter(BasicHeaderProcessor.java:93)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:67)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:90)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:171)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:82)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:533)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:146)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:524)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:257)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1595)
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:255)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1340)
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:203)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:473)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1564)
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:201)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1242)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:144)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
at org.eclipse.jetty.server.Server.handle(Server.java:503)
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:364)
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:260)
at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:305)
at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103)
at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:118)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:333)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:310)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:168)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:126)
at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:366)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:765)
at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:683)
at java.lang.Thread.run(Thread.java:748)

### Problem description

I'am trying to trigger a build on Jenkins when my pipeline on Gitlab is successful
- what was expected: when a pipeline ends successful on Gitlab it should trigger build on Jenkins.
- when I test the Webhooks on Gitlab with pipeline event it returns 200 code but no job is started on Jenkins. When there is a new commit/push on the repo and the Gitlab pipeline stars I see on Webhook logs 200 codes but once the pipeline ends on success I get 500 from Jenkins saying "sourceProjectId must not be null" as in the logs below.