[SPARK-21205][SQL] pmod(number, 0) should be null.

[wangyum]

What changes were proposed in this pull request?

Hive pmod(3.13, 0):

hive> select pmod(3.13, 0);
OK
NULL
Time taken: 2.514 seconds, Fetched: 1 row(s)
hive> 

Spark mod(3.13, 0):

spark-sql> select mod(3.13, 0);
NULL
spark-sql> 

But the Spark pmod(3.13, 0):

spark-sql> select pmod(3.13, 0);
17/06/25 09:35:58 ERROR SparkSQLDriver: Failed in [select pmod(3.13, 0)]
java.lang.NullPointerException
	at org.apache.spark.sql.catalyst.expressions.Pmod.pmod(arithmetic.scala:504)
	at org.apache.spark.sql.catalyst.expressions.Pmod.nullSafeEval(arithmetic.scala:432)
	at org.apache.spark.sql.catalyst.expressions.BinaryExpression.eval(Expression.scala:419)
	at org.apache.spark.sql.catalyst.expressions.UnaryExpression.eval(Expression.scala:323)
...

This PR make pmod(number, 0) to null.

How was this patch tested?

unit tests

[SparkQA]

Test build #78572 has finished for PR 18413 at commit ffd3bcb.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

I don't know enough to review the change but I believe you're correct. Dividing by zero also results in NULL right?

[SparkQA]

Test build #78584 has finished for PR 18413 at commit 9bad90f.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #78587 has finished for PR 18413 at commit 508c3aa.

• This patch fails PySpark pip packaging tests.
• This patch merges cleanly.
• This patch adds no public classes.

[gatorsmile]

cc @wzhfy

[wangyum]

Jenkins, retest this please

[SparkQA]

Test build #78785 has finished for PR 18413 at commit 508c3aa.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[wangyum]

Jenkins, retest this please

[SparkQA]

Test build #78911 has finished for PR 18413 at commit 508c3aa.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #79073 has finished for PR 18413 at commit da037c8.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[wangyum]

Jenkins, retest this please

[SparkQA]

Test build #79087 has finished for PR 18413 at commit da037c8.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[wangyum]

@HyukjinKwon Could you help review this?

[hvanhovell]

retest this please

[SparkQA]

Test build #80240 has finished for PR 18413 at commit da037c8.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[hvanhovell]

LGTM - merging to master