Error in EM while upgrading on farm the application, leading to unapplied migration

[oanalavinia]

Steps to reproduce

1. Have Diagram Application (Pro) 1.10 installed on farm
2. Create a diagram with clipart shapes
   
3. Upgrade on farm the application to version 1.15.2
4. Observe the progress displayed in Extension Manager
5. Observe the created diagram page

Results
The following error appears, but the application is upgraded correctly:

Failed to send event [org.xwiki.extension.event.ExtensionUpgradedEvent@4cd30ffd] to listener [com.xwiki.diagram.internal.DiagramApplicationListener@766a17a5]
class java.lang.NullPointerException: null
    at com.xwiki.diagram.internal.DiagramApplicationListener.getTargetWikis(DiagramApplicationListener.java:80)
    at com.xwiki.diagram.internal.DiagramApplicationListener.onEvent(DiagramApplicationListener.java:75)
    at org.xwiki.observation.internal.DefaultObservationManager.notify(DefaultObservationManager.java:304)
    at org.xwiki.observation.internal.DefaultObservationManager.notify(DefaultObservationManager.java:269)
    at org.xwiki.extension.job.internal.AbstractExtensionJob.installExtension(AbstractExtensionJob.java:339)
    at org.xwiki.extension.job.internal.AbstractExtensionJob.applyAction(AbstractExtensionJob.java:209)
    at org.xwiki.extension.job.internal.AbstractExtensionJob.applyActions(AbstractExtensionJob.java:157)
    at org.xwiki.extension.job.internal.InstallJob.runInternal(InstallJob.java:154)
    at org.xwiki.job.AbstractJob.runInContext(AbstractJob.java:206)
    at org.xwiki.job.AbstractJob.run(AbstractJob.java:189)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

This error appears in EM despite the version from which the upgrade is done.

After upgrade, the created page is broken:

[oanalavinia]

The unapplied migration will affect only diagrams created before Diagram Application version 1.11, but the error in EM will appear for any upgrade

[oanalavinia]

Note that to have the fix to the problem, two diagram upgrades will be needed, where the first upgrade is to a version >= 1.15.3 (the fix version).

The reason is that a component that listens to the upgrade operation is the provider of the error, and while doing the first upgrade the old component will be the one registered. Only on a second upgrade the new listener (that was fixed in the previous upgrade) will be the one registered.