apache/spark — pull request #861 by ueshin (2014-05-23 10:43:43+00:00)
Title: [SPARK-1914] [SQL] Simplify CountFunction not to traverse to evaluate all child expressions.

`CountFunction` should count up only if the child's evaluated value is not null.

Because it traverses to evaluate all child expressions, even if the child is null, it counts up if one of the all children is not null.