CreateMap allows non-unique keys

Spark-Sql, CreateMap does not enforce unique keys, i.e. it's possible to create a map with two identical keys:

CreateMap(Literal(1), Literal(11), Literal(1), Literal(12))

This does not behave like standard maps in common programming languages.
proper behavior should be chosen:

1. first 'wins'
2. last 'wins'
3. runtime error.

GetMapValue currently implements option #1. Even if this is the desired behavior CreateMap should return a unique map.