Note that dowstream-ext is the JIRA component for this plugin: http://wiki.jenkins-ci.org/display/JENKINS/Downstream-Ext+Plugin

Therefore unassigned this issue from downstream-ext - currently there's no component for downstream buildview

Now there is a component for it.

This problem becomes very urgent at our site as
a) the plugin is not usable at the moment
b) some projects are in need for it
c) since Hudson 1.355 we have to completly uninstall it
(before we just deactivated it but Hudson 1.355 now hangs)

Would it be possible to provide at least a quick fix which does a null check and in the case just does nothing?

If this view would be wrong in some cases it would be even better than not having it at all.

I realized that if I uninstall the plugin hudson hangs because of an entry in the build.xml of the several job runs:
<org.jvnet.hudson.plugins.DownstreamBuildViewAction>
<build class="hudson.maven.MavenModuleSetBuild" reference="../../.."/>
</org.jvnet.hudson.plugins.DownstreamBuildViewAction>

Now I have to remove this entry out of EVERY existing build.xml in order to keep hudson running.

it seems that is (at least often) happens when a release is made. On normal Snapshot builds afair I did not see this behavior.

This error is also happening for us - we just started trying for the first time to get hudson to create our release builds as well. We get the problem with maven release builds with the current maven release plugin and hudson 1.362 unless we disable the downstream plugin. Normal builds work fine. The weird thing is we don't actually have downstream projects - what is failing is we have a parent pom that builds 4 modules in the same job. IN snapshot (normal build) all 4 show blue. In release mode only the first child module goes blue, the other 3 show red with the null pointer error. They have however successfully built on this supposedly failed build.

Ran into this bug by upgrading Hudson from 1.362 to 1.363

Started by upstream project "projectA" build number 899
FATAL: null
java.lang.NullPointerException
at org.jvnet.hudson.plugins.DownstreamBuildViewUpdateListener.onStarted(DownstreamBuildViewUpdateListener.java:84)
at org.jvnet.hudson.plugins.DownstreamBuildViewUpdateListener.onStarted(DownstreamBuildViewUpdateListener.java:48)
at hudson.model.listeners.RunListener.fireStarted(RunListener.java:139)
at hudson.model.Run.run(Run.java:1248)
at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:306)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:127)

This looks very similar to the http://issues.jenkins-ci.org/browse/JENKINS-7691 (Release Build is marked as failure for multi-module projects.) which is fixed in plugin version 1.5 could I kindly ask you to retest as I have not been able to reproduce the stacktrace lately?

No response, but yes, it was certainly a duplicate of JENKINS-7691.
So resolving as duplicate.