Is your feature request related to a problem or challenge? Please describe what you are trying to do.

It seems like converting a null column to other types should be trivially supported (all null values). Right now when operations require this, I need to have a function that creates an array of null values of the given data type.

Describe the solution you'd like
Casting an array with DataType::Null to any other type produces an array of the given type containing all null values.

Describe alternatives you've considered
None.

Additional context