private static String getSafeHost(String hostname) {
    return (null == hostname) ? INTERNAL_HOSTNAME : hostname;
  }
Helper to make sure the hostname is non-null for internal command map.
@param hostname  the hostname for the map key
@return the hostname when not {@code null}, otherwise {@link #INTERNAL_HOSTNAME}
ambari-server/src/main/java/org/apache/ambari/server/actionmanager/Stage.java