Attempting to push to an unauthenticated registry, and am getting:

FATAL: authConfig was not specified
java.lang.NullPointerException: authConfig was not specified
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:204)
at com.github.dockerjava.core.command.AbstrAuthCfgDockerCmd.withAuthConfig(AbstrAuthCfgDockerCmd.java:33)
at com.github.dockerjava.core.DockerClientImpl.pushImageCmd(DockerClientImpl.java:129)
at org.jenkinsci.plugins.dockerbuildstep.cmd.PushImageCommand.execute(PushImageCommand.java:72)
at org.jenkinsci.plugins.dockerbuildstep.DockerBuilder.perform(DockerBuilder.java:78)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:770)
at hudson.model.Build$BuildExecution.build(Build.java:199)
at hudson.model.Build$BuildExecution.doRun(Build.java:160)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:533)
at hudson.model.Run.execute(Run.java:1745)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
at hudson.model.ResourceController.execute(ResourceController.java:89)
at hudson.model.Executor.run(Executor.java:240)

No authentication is needed for this registry, and none is specified in Jenkins.

Thanks.