Install latest perforce plugin
->Manage Jenkins
->Configure System
->leave default user/pass blank for perforce
->click save
(crash)

->enter "test" for default user/pass for perforce
->click save
(ok)

Caused by: java.lang.NullPointerException
at hudson.plugins.perforce.PerforcePasswordEncryptor.appearsToBeAnEncryptedPassword(PerforcePasswordEncryptor.java:30)
at hudson.plugins.perforce.PerforceSCM$PerforceSCMDescriptor.setDefaultP4Passwd(PerforceSCM.java:1929)
at hudson.plugins.perforce.PerforceSCM$PerforceSCMDescriptor.configure(PerforceSCM.java:1961)
at jenkins.model.Jenkins.configureDescriptor(Jenkins.java:2898)
at jenkins.model.Jenkins.doConfigSubmit(Jenkins.java:2861)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:622)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:298)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:161)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:96)
at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:121)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:745)
... 61 more