Setting DefaultMissingValueReplacement after using any of the convenience constructors that automatically call the .Learn method will result in DefaultMissingValueReplacement being ignored.

Either we have to mark some of the convenience constructors as obsolete (as they are a leftover of the old API where the .Learn() method was not available), or update the ColumnOptions to keep a reference to the parent Codification object and track what is the current default just before the moment when data needs to be transformed.