NPE during cleanup -> PDF renaming

[koppor]

JabRef 2016-02-28--master--a0444ab

I have following bib entry:

@Article{MLU2011,
  author =        {Ralph Mietzner and Frank Leymann and Tobias Unger},
  title =         {Horizontal and vertical combination of multi-tenancy patterns in service-oriented applications},
  journal =       {Enterprise Information Systems},
  year =          {2011},
  volume =        {5},
  number =        {1},
  pages =         {59--77},
  month =         feb,
  doi =           {10.1080/17517575.2010.492950},
  file =          {:Veröffentlichungen\\ART-2010-06 - Patterns Journal Version.pdf:PDF},
  publisher =     {Informa {UK} Limited}
}

(The wrong indent is solved by #851)

I do a cleanup on that entry with "Rename PDFs to given filename format pattern" only. The file does not get renamed, but a NPE is risen.

Side comment: The status box still shows "Doing a cleanup for entries..." and does not show "Error during cleanup" (or "Error" or something similar).

14:22:11.427 [AWT-EventQueue-0] ERROR net.sf.jabref.gui.BasePanel - runCommand error: null
java.lang.NullPointerException
    at java.util.Objects.requireNonNull(Unknown Source) ~[?:1.8.0_66]
    at net.sf.jabref.logic.layout.LayoutHelper.<init>(LayoutHelper.java:59) ~[JabRef-dev-fat.jar:?]
    at net.sf.jabref.util.Util.getLinkedFileName(Util.java:207) ~[JabRef-dev-fat.jar:?]
    at net.sf.jabref.logic.cleanup.RenamePdfCleanup.cleanup(RenamePdfCleanup.java:66) ~[JabRef-dev-fat.jar:?]
    at net.sf.jabref.logic.cleanup.CleanupWorker.cleanup(CleanupWorker.java:64) ~[JabRef-dev-fat.jar:?]
    at net.sf.jabref.gui.actions.CleanupAction.doCleanup(CleanupAction.java:161) ~[JabRef-dev-fat.jar:?]
    at net.sf.jabref.gui.actions.CleanupAction.run(CleanupAction.java:106) ~[JabRef-dev-fat.jar:?]
    at sun.reflect.GeneratedMethodAccessor23.invoke(Unknown Source) ~[?:?]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_66]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_66]
    at spin.Invocation.evaluate(Invocation.java:175) ~[JabRef-dev-fat.jar:?]
    at spin.off.SpinOffEvaluator$1.run(SpinOffEvaluator.java:108) ~[JabRef-dev-fat.jar:?]
    at java.lang.Thread.run(Unknown Source) ~[?:1.8.0_66]