Failure building Javadoc when JAVA_HOME is empty

To reproduce:

1. export JAVA_HOME=
2. /opt/apache-maven-3.0.5/bin/mvn clean install -DskipTests -f ./ArjunaJTA/narayana-jta/pom.xml

It also happens if you use the maven version in tools/maven (also version 3.0.5).

This doesn't fail:

1. export JAVA_HOME=
2. /opt/apache-maven-3.0.3/bin/mvn clean install -DskipTests -f ./ArjunaJTA/narayana-jta/pom.xml

Currently only seen this on a Mac. Would be good if a linux user could try to reproduce.

Maven 3.0.5 is the latest release. I've not found a known issue for this, but it is hard to search for.