public static boolean isValidTxn(long txnId) {
    return txnId != 0;
  }
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