This module maps classes used in field type definitions to the custom definable field in Mongoid.
Get the custom field type for the provided class used in the field definition.
@example Get the mapping for the class.
Mappings.for(BSON::ObjectId)
@param [ Class ] klass The class to get the field type for.
@return [ Class ] The class of the custom field.
@since 2.1.0
[Validate]