... with a test case. The fix is in Stapler.

Now to check behavior in trunk.

[JENKINS-3265] [JENKINS-17341] Even if older plugins throw an NPE during reload, continue loading job.

removed the noAnime() conversions, so we can rely on the compiler to warn us, if we forget a case here

Add convenience method for checking if object is MatrixProject

[FIXED JENKINS-18671] Clock Difference broken on Manage Nodes page

against incorrect values if times are ever compared between different JVM nodes

System.nanos() returns a monotonically increasing value that is not related
to wallclock time. Use System.currentTimeMillis() instead.

Unlike the bug I originally reproduced, in which the parent had some builds
but the context in which the new build was scheduled omits a parent,
this seems to be due to a case in which there is no build record at all for the parent.
No idea how that could happen (getLastBuild should return even a running, failed, or aborted build),
but @treydock reports a stack trace in 1.509.2 which implies this.
So fixing null safety; will not prevent an exception but will report it more gracefully.

Going back in browser history can reset configuration form to the *previous* state,
not what was just saved! (In the case of lazily inserted form elements.)
Thus clicking Save from that page would actually revert your recent changes.
For now, just omitting the button; could make it go back to index or configuration pages,
but there are already links for this.