SVN: NullPointerException when updating externals to workspace with format version < 1.6

     if (SVNEventAction.SKIP.equals(action))
        {
            SVNErrorMessage err = event.getErrorMessage();


            if (SVNEventAction.UPDATE_EXTERNAL.equals(event.getExpectedAction()))
            {
                if (SVNErrorCode.WC_LOCKED.equals(err.getErrorCode())) // NPE here
                {
                    log_error("Update of external at '" + file + "' failed because it is locked.");
                    throw new ExternalsLockException(err, file);
                }