I got a status code 500 while switching from the default ref spec to a custom ref spec. Note the NullPointerException down at the bottom. This may not be hard for someone who knows the code to fix.

I don't think this is related to JENKINS-14707, but may be in the same area of the code.

Status Code: 500

Exception: java.lang.RuntimeException: Failed to instantiate class hudson.plugins.git.GitSCM from {"value":"2","userRemoteConfigs":

{"url":"ssh://use.your.own","name":"ANONADemo","refspec":"+refs/heads/master:refs/remotes/ANONADemo/master"}

,"branches":

{"name":"**"}

,"includedRegions":"","excludedRegions":"","excludedUsers":"","localBranch":"","relativeTargetDir":"ANONADemo","reference":"","scmName":"","gitConfigName":"","gitConfigEmail":"","pruneBranches":false,"skipTag":false,"clean":false,"remotePoll":false,"disableSubmodules":false,"recursiveSubmodules":false,"authorOrCommitter":false,"wipeOutWorkspace":false,"ignoreNotifyCommit":false,"useShallowClone":false,"":["","auto"],"gitTool":"Default"}
Stacktrace:
javax.servlet.ServletException: java.lang.RuntimeException: Failed to instantiate class hudson.plugins.git.GitSCM from {"value":"2","userRemoteConfigs":

{"url":"ssh://use.your.own/gitroot/supertrees/ANONADemo","name":"ANONADemo","refspec":"+refs/heads/master:refs/remotes/ANONADemo/master"}

,"branches":

{"name":"**"}

,"includedRegions":"","excludedRegions":"","excludedUsers":"","localBranch":"","relativeTargetDir":"ANONADemo","reference":"","scmName":"","gitConfigName":"","gitConfigEmail":"","pruneBranches":false,"skipTag":false,"clean":false,"remotePoll":false,"disableSubmodules":false,"recursiveSubmodules":false,"authorOrCommitter":false,"wipeOutWorkspace":false,"ignoreNotifyCommit":false,"useShallowClone":false,"":["","auto"],"gitTool":"Default"}
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:719)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:770)
at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:241)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:677)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:770)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:583)
at org.kohsuke.stapler.Stapler.service(Stapler.java:214)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:95)
at hudson.plugins.scm_sync_configuration.extensions.ScmSyncConfigurationFilter$1.call(ScmSyncConfigurationFilter.java:36)
at hudson.plugins.scm_sync_configuration.ScmSyncConfigurationDataProvider.provideRequestDuring(ScmSyncConfigurationDataProvider.java:103)
at hudson.plugins.scm_sync_configuration.extensions.ScmSyncConfigurationFilter.doFilter(ScmSyncConfigurationFilter.java:32)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:98)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:87)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:48)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:124)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.basicauth.BasicProcessingFilter.doFilter(BasicProcessingFilter.java:174)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.ApiTokenFilter.doFilter(ApiTokenFilter.java:64)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:66)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:50)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:309)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.RuntimeException: Failed to instantiate class hudson.plugins.git.GitSCM from {"value":"2","userRemoteConfigs":

{"url":"ssh://use.your.own/gitroot/supertrees/ANONADemo","name":"ANONADemo","refspec":"+refs/heads/master:refs/remotes/ANONADemo/master"}

,"branches":

{"name":"**"}

,"includedRegions":"","excludedRegions":"","excludedUsers":"","localBranch":"","relativeTargetDir":"ANONADemo","reference":"","scmName":"","gitConfigName":"","gitConfigEmail":"","pruneBranches":false,"skipTag":false,"clean":false,"remotePoll":false,"disableSubmodules":false,"recursiveSubmodules":false,"authorOrCommitter":false,"wipeOutWorkspace":false,"ignoreNotifyCommit":false,"useShallowClone":false,"":["","auto"],"gitTool":"Default"}
at hudson.model.Descriptor.newInstance(Descriptor.java:602)
at hudson.plugins.git.GitSCM$DescriptorImpl.newInstance(GitSCM.java:1502)
at hudson.plugins.git.GitSCM$DescriptorImpl.newInstance(GitSCM.java:1423)
at hudson.scm.SCMS.parseSCM(SCMS.java:63)
at hudson.model.AbstractProject.submit(AbstractProject.java:1921)
at hudson.model.Project.submit(Project.java:195)
at hudson.model.Job.doConfigSubmit(Job.java:1082)
at hudson.model.AbstractProject.doConfigSubmit(AbstractProject.java:742)
at sun.reflect.GeneratedMethodAccessor906.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:288)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:151)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:90)
at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:111)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:677)
... 63 more
Caused by: java.lang.NullPointerException
at hudson.plugins.git.GitSCM.<init>(GitSCM.java:250)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
at org.kohsuke.stapler.RequestImpl.invokeConstructor(RequestImpl.java:438)
at org.kohsuke.stapler.RequestImpl.access$200(RequestImpl.java:76)
at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:594)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:391)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:387)
at hudson.model.Descriptor.newInstance(Descriptor.java:593)
... 79 more