I have added a post build step of create image / build image. Get the following
ERROR: Build step failed with exception
java.lang.NullPointerException: uri was not specified
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:204)
at com.github.dockerjava.core.DockerClientConfig$DockerClientConfigBuilder.withUri(DockerClientConfig.java:406)
at org.jenkinsci.plugins.dockerbuildstep.DockerBuilder$DescriptorImpl.createDockerClient(DockerBuilder.java:120)
at org.jenkinsci.plugins.dockerbuildstep.DockerBuilder$DescriptorImpl.getDockerClient(DockerBuilder.java:204)
at org.jenkinsci.plugins.dockerbuildstep.DockerBuilder.perform(DockerBuilder.java:68)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:779)
at hudson.maven.MavenModuleSetBuild$MavenModuleSetBuildExecution.build(MavenModuleSetBuild.java:919)
at hudson.maven.MavenModuleSetBuild$MavenModuleSetBuildExecution.doRun(MavenModuleSetBuild.java:870)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:534)
at hudson.model.Run.execute(Run.java:1741)
at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:531)
at hudson.model.ResourceController.execute(ResourceController.java:98)
at hudson.model.Executor.run(Executor.java:410)
Build step 'Execute Docker command' marked build as failure
channel stopped

I have now installed docker on to the Jenkins machine. Made no difference.
What am I doing wrong. I do think the documentation could be improved on the home page for this plugin.