This is a simple little bug.

When:
Publish Clover PHP Coverage Report
is checked, but the
Clover XML Location
field is empty, the following NPE is thrown during the build:

Publishing Clover coverage report...
ERROR: Publisher org.jenkinsci.plugins.cloverphp.CloverPublisher aborted due to exception java.lang.NullPointerException
at hudson.FilePath.isAbsolute(FilePath.java:226)
at hudson.FilePath.<init>(FilePath.java:214)
at hudson.FilePath.child(FilePath.java:896)
at org.jenkinsci.plugins.cloverphp.CloverPublisher.copyXmlReport(CloverPublisher.java:236)
at org.jenkinsci.plugins.cloverphp.CloverPublisher.perform(CloverPublisher.java:177)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:662)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:638)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:616)
at hudson.model.Build$RunnerImpl.post2(Build.java:161)
at hudson.model.AbstractBuild$AbstractRunner.post(AbstractBuild.java:585)
at hudson.model.Run.run(Run.java:1398)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:145)

I am happy to provide more information if necessary.