public static String nvl(String input) {
    return input != null ? " = ? " : " IS NULL ";
  }
A helper method to return SQL's 'IS NULL'
clause whenever input is NULL.
@param input A string to be compared to null.
@return String
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/txn/TxnUtils.java