[SPARK-30303][SQL] Fix match error in percentile function when the percentage is null

[yaooqinn]

What changes were proposed in this pull request?

Similar to #26905

spark-sql> select percentile(1, null);
19/12/19 16:35:04 ERROR SparkSQLDriver: Failed in [select percentile(1, null)]
scala.MatchError: null


spark-sql> select percentile(1, array(0.0, null)); -- null is illegal but treat as zero

Why are the changes needed?

bugfix

Does this PR introduce any user-facing change?

yes, select percentile(1, null); throws AnalysisException instead.

How was this patch tested?

add ut

[yaooqinn]

cc @cloud-fan the problem of percentile is similar to percentile_approx

[SparkQA]

Test build #115552 has finished for PR 26947 at commit e0e0591.

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

[SparkQA]

Test build #115571 has finished for PR 26947 at commit be330eb.

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

[srowen]

Let's fix it in one JIRA/PR if they're this related

[dongjoon-hyun]

+1 for @srowen 's advice.

[maropu]

+1, too, for easy-to-reviews.

[yaooqinn]

merged to #26905, thanks for your suggestions.