analyzing groovy-all-2.2.1-indy.jar with FindBugs-2.0.3 I get (at the end of phase 2) an ArrayIndexOutOfBoundException: null , but no other detail sorry ...
Note that analyzing the standard version (not specific for Java 7) of that jar works good (it's in the same folder).
You can find that jar in the standard download of Groovy (for example from here: http://dist.groovy.codehaus.org/distributions/groovy-binary-2.2.1.zip , under the folder embeddable ).
I'm on Windows and I'm using JDK 7 Update 40 at 64 bit.
Tell me if you need more info.
Thanks a lot (FindBugs is a great tool !!).