When I upgraded Subversion Plugin from 1.18 to 1.19 I could not connect to svn anymore.

The Exception was:
java.lang.reflect.UndeclaredThrowableException
at hudson.scm.$Proxy6.getCredential(Unknown Source)
at hudson.scm.SubversionSCM$DescriptorImpl$SVNAuthenticationProviderImpl.fromProvider(SubversionSCM.java:1560)
at hudson.scm.SubversionSCM$DescriptorImpl$SVNAuthenticationProviderImpl.requestClientAuthentication(SubversionSCM.java:1570)
at org.tmatesoft.svn.core.internal.wc.DefaultSVNAuthenticationManager.getFirstAuthentication(DefaultSVNAuthenticationManager.java:204)
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:549)
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:275)
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:263)
at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.exchangeCapabilities(DAVConnection.java:516)
at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.open(DAVConnection.java:98)
at org.tmatesoft.svn.core.internal.io.dav.DAVRepository.openConnection(DAVRepository.java:1001)
at org.tmatesoft.svn.core.internal.io.dav.DAVRepository.getRepositoryUUID(DAVRepository.java:146)
at org.tmatesoft.svn.core.wc.SVNBasicClient.createRepository(SVNBasicClient.java:342)
at org.tmatesoft.svn.core.wc.SVNBasicClient.createRepository(SVNBasicClient.java:330)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.update(SVNUpdateClient.java:535)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.doUpdate(SVNUpdateClient.java:401)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:635)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:596)
at hudson.FilePath$FileCallableWrapper.call(FilePath.java:1899)
at hudson.remoting.UserRequest.perform(UserRequest.java:114)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:270)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.io.IOException: Unable to serialize hudson.scm.SubversionSCM$DescriptorImpl$PasswordCredential@67ac3d0c
at hudson.remoting.UserRequest.serialize(UserRequest.java:162)
at hudson.remoting.UserRequest.perform(UserRequest.java:122)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:270)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.io.NotSerializableException: hudson.util.Secret
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1156)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1474)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1392)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1150)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:326)
at hudson.remoting.UserRequest._serialize(UserRequest.java:151)
at hudson.remoting.UserRequest.serialize(UserRequest.java:160)
... 9 more

Now I downgraded to 1.18 and everything works fine again.