I don't know anything about it directly, but seems like it would have been caused by https://github.com/apache/spark/commit/e3201e165e41f076ec72175af246d12c0da529cf The "?" in fromClause is what's generating the warning, and it may be ignorable.
On Mon, May 14, 2018 at 12:38 AM Reynold Xin <r...@databricks.com> wrote: > Just saw this in one of my PR that's doc only: > > [error] warning(154): SqlBase.g4:400:0: rule fromClause contains an optional > block with at least one alternative that can match an empty string > > > >
