After upgrade to:

Jenkins 1.523
Ivy-Plugin 1.23.1

All Ivy-Projects will not build anymore and ends up with a NPE. Checkout from SVN is fine so far:

Building in workspace /var/lib/jenkins/jobs/graphicsUtility/workspace
Cleaning local Directory .
Checking out svn+ssh://ziv@uz-labor/var/svn/java-libs/graphicsUtility/trunk at revision '2013-07-19T15:06:03.638 +0200'
[...]
U .
At revision 752
no change for svn+ssh://ziv@uz-labor/var/svn/java-libs/graphicsUtility/trunk since the previous build
ERROR: Processing failed due to a bug in the code. Please report this to users@hudson.dev.java.net
java.lang.NullPointerException
at hudson.FilePath.isAbsolute(FilePath.java:239)
at hudson.FilePath.resolvePathIfRelative(FilePath.java:224)
at hudson.FilePath.<init>(FilePath.java:220)
at hudson.FilePath.child(FilePath.java:1133)
at hudson.ivy.IvyModuleSetBuild$RunnerImpl.doRun(IvyModuleSetBuild.java:372)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:586)
at hudson.model.Run.execute(Run.java:1593)
at hudson.model.Run.run(Run.java:1539)
at hudson.ivy.IvyModuleSetBuild.run(IvyModuleSetBuild.java:281)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:247)
project=hudson.ivy.IvyModuleSet@17feafba[graphicsUtility]
project.getModules()=[hudson.ivy.IvyModule@72a32604[graphicsUtility/de.unicomp:graphicsUtility]]
FATAL: null
java.lang.NullPointerException
at hudson.FilePath.isAbsolute(FilePath.java:239)
at hudson.FilePath.resolvePathIfRelative(FilePath.java:224)
at hudson.FilePath.<init>(FilePath.java:220)
at hudson.FilePath.child(FilePath.java:1133)
at hudson.ivy.IvyModuleSetBuild$RunnerImpl.doRun(IvyModuleSetBuild.java:372)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:586)
at hudson.model.Run.execute(Run.java:1593)
at hudson.model.Run.run(Run.java:1539)
at hudson.ivy.IvyModuleSetBuild.run(IvyModuleSetBuild.java:281)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:247)