correctly set FieldOptions default_null in table proto
This should correct the following problem:
drizzle> create table e ( b int DEFAULT NULL); Query OK, 0 rows affected (0.01 sec)
drizzle> show fields from e; +-------+---------+------+---------+-----------------+ | Field | Type | Null | Default | Default is NULL | +-------+---------+------+---------+-----------------+ | b | INTEGER | TRUE | | FALSE | +-------+---------+------+---------+-----------------+ 1 row in set (0 sec)
drizzle> show create table e; +-------+-----------------------------------------------------------+ | Table | Create Table | +-------+-----------------------------------------------------------+ | e | CREATE TABLE `e` ( `b` int DEFAULT NULL ) ENGINE=InnoDB | +-------+-----------------------------------------------------------+ 1 row in set (0 sec)