filefault-package:format-xml fails when executed in build reactor

The format-xml fails with a "basedir not set" exception when being executed in the root of a multi module maven project (build reactor). 

Assuming the following structure:

<project>/ 
 - pom.xml
 a/
  - pom.xml
  src/main/content/jcr_root/
 b/
  - pom.xml
  src/main/content/jcr_root/

I want to execute mvn filefault-package:format-xml from the top level <project>. 

The reason is that 

AbstractSourceAndMetadataPackageMojo.getFirstExistingDirectory() returns null when non of the configured jcrRootSourceDirectory exists and this null is passed unchecked to a org.codehaus.plexus.util.DirectoryScanner which validates the given basedir and if not set throws ans ISE.