This doesn't relate to the StackMapTable attribute. For compatibility reason,
the VM only checks newly added rules in JDK 6 for class files with version >=50.
Therefore the error only occurs in target 6.
This regression is caused by the fix of 4012001, in which the VM enforces all
interfaces to be abstract for class files with version >=50. Although javac
ensures that the interfaces it generates are abstract, it doesn't do so for
the inner classes it reads from other sources. In this case, the inner class
Enter is read from the old collection archive, which doesn't have its "abstract"