DeployProcessTask fails with a NullPointerException

Issue

Using DeployProcessTask with the process attribute results in a NullPointerException.

<taskdef name="deploypar" classname="org.jbpm.ant.DeployProcessTask"> 
  <classpath refid="exec-classpath" /> 
</taskdef> 
<deploypar process="test.par"/>

DeployProcessTask/build.xml:22: java.lang.NullPointerException
at org.jbpm.ant.DeployProcessTask.execute(DeployProcessTask.java:62)