public void addRole(String key, String role) {
   if (_roleAssignments == null) {
     _roleAssignments = new StringSetMap();
   }
   _roleAssignments.put(key, role);
 }
 public void removeRole(String key, String role) {
   if (_roleAssignments != null) {
     _roleAssignments.remove(key, role);
   }
 }
 public Set<String> getRoleSet(String key) {
   if (null != _roleAssignments) {
     return _roleAssignments.get(key);
   }
   return null;
 }