When running with Jenkins slaves and the branches are located on the slaves the rebase and integration jobs fail with the following exception:

hudson.util.IOException2: remote file operation failed: **\Jenkins-Slave\workspace\Project** at hudson.remoting.Channel@31943194:Jenkins-Slave-1
at hudson.FilePath.act(FilePath.java:779)
at hudson.FilePath.act(FilePath.java:765)
at jenkins.plugins.svnmerge.FeatureBranchProperty.rebase(FeatureBranchProperty.java:148)
at jenkins.plugins.svnmerge.RebaseAction.perform(RebaseAction.java:105)
at jenkins.plugins.svnmerge.RebaseAction.perform(RebaseAction.java:25)
at jenkins.plugins.svnmerge.AbstractSvnmergeTaskAction$WorkerThread.perform(AbstractSvnmergeTaskAction.java:105)
at hudson.model.TaskThread.run(TaskThread.java:127)
at jenkins.plugins.svnmerge.AbstractSvnmergeTaskAction$TaskImpl$1.run(AbstractSvnmergeTaskAction.java:161)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:238)
Caused by: java.io.IOException: Unable to serialize hudson.FilePath$FileCallableWrapper@d420d42
at hudson.remoting.UserRequest.serialize(UserRequest.java:166)
at hudson.remoting.UserRequest.<init>(UserRequest.java:62)
at hudson.remoting.Channel.call(Channel.java:680)
at hudson.FilePath.act(FilePath.java:772)
... 9 more
Caused by: java.io.NotSerializableException: jenkins.plugins.svnmerge.FeatureBranchProperty
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1167)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1520)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1485)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1403)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1161)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1520)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1485)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1403)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1161)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:337)
at hudson.remoting.UserRequest._serialize(UserRequest.java:155)
at hudson.remoting.UserRequest.serialize(UserRequest.java:164)
... 12 more

I tried to download the source code and make all classes Serializable, but I then got another exception:
java.lang.NullPointerException
at jenkins.plugins.svnmerge.FeatureBranchProperty.getUpstreamProject(FeatureBranchProperty.java:84)
at jenkins.plugins.svnmerge.FeatureBranchProperty.getUpstreamSubversionLocation(FeatureBranchProperty.java:88)
at jenkins.plugins.svnmerge.FeatureBranchProperty.getUpstreamURL(FeatureBranchProperty.java:102)
at jenkins.plugins.svnmerge.FeatureBranchProperty$1.invoke(FeatureBranchProperty.java:167)
at jenkins.plugins.svnmerge.FeatureBranchProperty$1.invoke(FeatureBranchProperty.java:153)
at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2030)
at hudson.remoting.UserRequest.perform(UserRequest.java:118)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:287)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:452)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:314)
at java.util.concurrent.FutureTask.run(FutureTask.java:149)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:896)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at hudson.remoting.Engine$1$1.run(Engine.java:60)
at java.lang.Thread.run(Thread.java:735)