HIVE-12727 introduces three new configurations to replace the existing hive.mapred.mode, which is deprecated. However, the default value for the latter is 'nonstrict', which prevent the new configurations from being used (see comments in that JIRA for more details).
This proposes to change the default value for hive.mapred.mode to null. Users can then set the three new configurations to get more fine-grained control over the strict checking. If user want to use the old configuration, they can set hive.mapred.mode to strict/nonstrict.