I think the NPE is just coincidence.

$ bin/jruby.indy -J-XX:+UseSerialGC test/test_rexml_document.rb
gamma is /export/twisti/hotspot-comp/hotspot/build/solaris_sparc_compiler2/fastdebug/gamma
java version "1.7.0-ea-fastdebug"
Java(TM) SE Runtime Environment (build 1.7.0-ea-fastdebug-b111)
OpenJDK Server VM (build 20.0-b01-internal-fastdebug, mixed mode)
OpenJDK Server VM (20.0-b01-internal-fastdebug) for solaris-sparc JRE (1.7.0), built on Oct 7 2010 06:40:38 by "ct232829" with Sun Studio 12u1
gamma -Djruby.memory.max=500m -Djruby.stack.max=1024k -Djruby.compile.invokedynamic=true -XX:+UnlockExperimentalVMOptions -XX:+EnableMethodHandles -XX:+EnableInvokeDynamic -Xmx500m -Xss1024k -Djffi.boot.library.path=./lib/native/sparc-SunOS:./lib/native/sparcv9-SunOS -XX:+UseSerialGC -Xbootclasspath/a:./lib/jruby.jar -classpath ./lib/profile.jar: -Djruby.home=. -Djruby.lib=./lib -Djruby.script=jruby -Djruby.shell=/bin/sh org.jruby.Main test/test_rexml_document.rb
VM option '+UnlockExperimentalVMOptions'
VM option '+EnableMethodHandles'
VM option '+EnableInvokeDynamic'
VM option '+UseSerialGC'
Loaded suite test/test_rexml_document
Started
E.
Finished in 39.261 seconds.

  1) Error:
test_entity_expansion_limit(TestRexmlDocument):
REXML::ParseException: #<REXML::ParseException: java.lang.NullPointerException
ruby.jit.match_C68C412E93A504F03A3CBA42B13990AAA32E83EB.__file__(source.rb:105)
ruby.jit.match_C68C412E93A504F03A3CBA42B13990AAA32E83EB.__file__(source.rb)
org.jruby.ast.executable.AbstractScript.__file__(AbstractScript.java:43)
org.jruby.internal.runtime.methods.JittedMethod.call(JittedMethod.java:187)
org.jruby.internal.runtime.methods.DefaultMethod.call(DefaultMethod.java:188)
org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:190)
<snip>