[SPARK-2295] [SQL] Make JavaBeans nullability stricter.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1235 from ueshin/issues/SPARK-2295 and squashes the following commits:

201c508 [Takuya UESHIN] Make JavaBeans nullability stricter.

(cherry picked from commit 32a1ad75313472b1b098f7ec99335686d3fe4fc3)
Signed-off-by: Michael Armbrust <michael@databricks.com>