Credentials not found for merge from mainline

svnmerge plugin 2.4, jenkins 1.595, matrix-based access control (with additional boxes checked), single module.

At the build step "Rebase with upstream Subversion revision" set to "Latest revision", I get the error:

13:24:06 [EnvInject] - Executing scripts and injecting environment variables after the SCM step.
...
13:24:06 [EnvInject] - Variables injected successfully.
13:24:06 FATAL: hudson.scm.SubversionSCM.createAuthenticationProvider(Lhudson/model/AbstractProject;Lhudson/scm/SubversionSCM$ModuleLocation;)Lorg/tmatesoft/svn/core/auth/ISVNAuthenticationProvider;
13:24:06 java.lang.NoSuchMethodError: hudson.scm.SubversionSCM.createAuthenticationProvider(Lhudson/model/AbstractProject;Lhudson/scm/SubversionSCM$ModuleLocation;)Lorg/tmatesoft/svn/core/auth/ISVNAuthenticationProvider;
13:24:06 at jenkins.plugins.svnmerge.FeatureBranchProperty.rebase(FeatureBranchProperty.java:162)
13:24:06 at jenkins.plugins.svnmerge.RebaseAction.perform(RebaseAction.java:115)
13:24:06 at jenkins.plugins.svnmerge.RebaseBuilder.perform(RebaseBuilder.java:50)
13:24:06 at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
13:24:06 at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:770)
13:24:06 at hudson.model.Build$BuildExecution.build(Build.java:199)
13:24:06 at hudson.model.Build$BuildExecution.doRun(Build.java:160)
13:24:06 at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:533)
13:24:06 at hudson.model.Run.execute(Run.java:1759)
13:24:06 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
13:24:06 at hudson.model.ResourceController.execute(ResourceController.java:89)
13:24:06 at hudson.model.Executor.run(Executor.java:240)

I'm not sure what this error is telling me. The original sync from the feature branch worked flawlessly. It would appear that it's trying to do some new authentication for the merge, but it's not clear why it's not getting credentials to use. Wouldn't it just be using the credentials from the feature branch sync?