maven throws a java.lang.NullPointerException at the end of a release:perform

I'm getting java.lang.NullPointerException when building when i reference maven-release-plugin in my pom.xml, It doesn't seem to matter which version of the plugin i reference. i'm using maven 2.2.1, java 1.6_23 on windows 7 64 bit. I can also repro on linux.

The only way it works without error is if I specify 2.0-beta-9 from the command line:
mvn org.apache.maven.plugins:maven-release-plugin:2.0-beta-9:perform -DconnectionUrl=..

It fails if I do this:
mvn org.apache.maven.plugins:maven-release-plugin:2.1:perform -DconnectionUrl=..

It also fails when I reference 2.0-beta-9 in my pom.xml then run:
mvn relase:perform -DconnectionUrl=..