SQOOP-598. Document NULL substitution string changes for HIVE import.
SQOOP-598. Document NULL substitution string changes for HIVE import.

(Jarek Jarcec Cecho via Abhijeet Gaikwad)

bonnetb/sqoop,icoding/sqoop,apache/sqoop,YaroslavLitvinov/sqoop,pkit/sqoop,baifendian/sqoop,bonnetb/sqoop,dlanza1/sqoop,YaroslavLitvinov/sqoop,rekhajoshm/sqoopfork,dlanza1/sqoop,dlanza1/parquet-mr,YaroslavLitvinov/sqoop,pkit/sqoop,rekhajoshm/sqoopfork,pkit/sqoop,rekhajoshm/sqoopfork,dlanza1/parquet-mr,icoding/sqoop,unicredit/sqoop,baifendian/sqoop,icoding/sqoop,unicredit/sqoop,unicredit/sqoop,baifendian/sqoop,dlanza1/sqoop,apache/sqoop,bonnetb/sqoop,apache/sqoop,dlanza1/parquet-mr