Code review request: 7086601 "Error message bug: cause for method mismatch is 'null'"

[Dmeetry Degrave]

hi,

I'm looking for a code review for 7086601. This is a backport from jdk8 
to 7u4 with identical fix.

bug: http://bugs.sun.com/view_bug.do?bug_id=7086601
webrev: http://cr.openjdk.java.net/~dmeetry/7086601/webrev.00
jdk8: http://hg.openjdk.java.net/jdk8/tl/langtools/rev/3a2200681d69

thanks,
dmeetry