Hive-on-MR deprecation warning is not diplayed when engine is set to capital letter 'MR'

hive> SET hive.execution.engine=mr;
Hive-on-MR is deprecated in Hive 2 and may not be available in the future versions. Consider using a different execution engine (i.e. tez, spark) or using Hive 1.X releases.
hive>

hive> SET hive.execution.engine=MR;
hive>

This warning seems to be generated only with small letter 'mr' wand not with capital letter "MR".

generateMrDeprecationWarning() seem to be displaying this warning and is being called in different classes.

Ex: https://github.com/apache/hive/blob/master/cli/src/java/org/apache/hadoop/hive/cli/CliDriver.java#L754

https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/Driver.java#L1900