apache/spark — pull request #532 by ueshin (2014-04-24 10:36:27+00:00)
Title: [SPARK-1608] [SQL] Fix Cast.nullable when cast from StringType to NumericType/TimestampType.

`Cast.nullable` should be `true` when cast from `StringType` to `NumericType` or `TimestampType`.
Because if `StringType` expression has an illegal number string or illegal timestamp string, the casted value becomes `null`.