spark git commit: [SPARK-19732][FOLLOW-UP] Document behavior changes made in na.fill and fillna

Repository: spark Updated Branches: refs/heads/branch-2.3 9ca0f6eaf -> f624850fe [SPARK-19732][FOLLOW-UP] Document behavior changes made in na.fill and fillna ## What changes were proposed in this pull request? https://github.com/apache/spark/pull/18164 introduces the behavior changes. We

spark git commit: [SPARK-19732][FOLLOW-UP] Document behavior changes made in na.fill and fillna

Repository: spark Updated Branches: refs/heads/master 76892bcf2 -> b46e58b74 [SPARK-19732][FOLLOW-UP] Document behavior changes made in na.fill and fillna ## What changes were proposed in this pull request? https://github.com/apache/spark/pull/18164 introduces the behavior changes. We need