Update json_value_body.typ

Solves null clob issue originally first seen when invoking json_dyn.executelist() on a table with null clobs.  Attempting to execute dbms_lob.read() on a null clob raises the following error:

ERROR: ORA-06502: PL/SQL: numeric or value error: invalid LOB locator specified: ORA-22275
Merge pull request #3 from Notsoswift/master

Fix null clob access in json_value_body.typ