code: @Override
  	public void mergePermissions(AccessControl from, AccessControl to)
  	{
  		if (from == null || to == null)
  			return;
  
  		List<Permission> otherPermissions = from.getPermissions();
  
  		if (otherPermissions == null)
  			return;
  
  		boolean changeNegative = from.isNegative() != to.isNegative();
  
  		if (changeNegative)
  			throw new SecurityException(
  			"Cannot change or mixed different negative property for ACL from:" + from + " to ACL:" + to
  			+ "  permission must be either all negative or all positive for a principal");
  
  		Iterator<Permission> i = otherPermissions.iterator();
  
  		while (i.hasNext())
  		{
  
  			to.addPermission(i.next());
  		}
  	}
docs: /*
  (non-Javadoc)
  
  @see
  nyla.solutions.core.security.data.Acl#mergePermissions(nyla.solutions.
  core.security.data.AccessControl,
  nyla.solutions.core.security.data.AccessControl)