java NullPointerException Error

One of my cronjob running error last night, the error message is the following, java.lang.NullPointerException    at UpdtCreatePrdIndex.translateStr(UpdtCreatePrdIndex.java:648)  Trace into the code, the error is in,  private static String translateStr(String trans_str) {        trans_str = trans_str.replaceAll(""","\"");        trans_str = trans_str.replaceAll("®","");        trans_str = trans_str.replaceAll("™","");        return trans_str }  Finally, find out the reason that we updated database table yesterday, and some field has value NULL. When those fields called this method, they failed.  NULL.replaceAll("a", "b") will cause  java.lang.NullPointerException