convert empty strings to null

My input file is a json file. I am loading that into a staging table. Then i am parsing the json using hive (Lateral view and json_tuple) and writing to a final avro table. My issue is some json values have empty strings. I want those empty strings to display as null.. what is the best way to achie

Fwd: UDF for MONTHS_BETWEEN

Is there currently a Hive UDF to mimic the Oracle function MONTHS_BETWEEN??