I'm using version 1.7 of the plugin, and while it seems to be working fine in most cases, a couple of pull requests consistently fail by

Caused by: java.lang.NullPointerException
at org.jenkinsci.plugins.ghprb.GhprbPullRequest.checkMergeable(GhprbPullRequest.java:168)
at org.jenkinsci.plugins.ghprb.GhprbPullRequest.check(GhprbPullRequest.java:68)
at org.jenkinsci.plugins.ghprb.GhprbRepository.onPullRequestHook(GhprbRepository.java:199)
at org.jenkinsci.plugins.ghprb.GhprbProjectAction.doIndex(GhprbProjectAction.java:56)
at sun.reflect.GeneratedMethodAccessor1734.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:288)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:151)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:90)
at org.kohsuke.stapler.MetaClass$2.dispatch(MetaClass.java:156)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:677)
... 64 more

I find this in the jenkins logs, as in the UI there is no track of the pull request (as it was never sent).

This was the failing pull request, in case it helps:
https://github.com/hibernate/hibernate-search/pull/407