[SUREFIRE-828] Fixing problems with missing empty-string check on groups/excludedGroups, especially in TestNG...this is the fixed code for TestNG, along with tests. The fix is disabled until I verify that the tests fail.
maven/surefire/trunk/surefire-integration-tests/src/test/java/org/apache/maven/surefire/its/jiras/Surefire828EmptyGroupExprIT.java
maven/surefire/trunk/surefire-integration-tests/src/test/resources/surefire-828-emptyGroupExpr-junit48/