Register the function converting it to MultiMap.innerMap's function type.
Vaidates both key and value before applying the function.
Vaidates both key and value before applying the function.
User values for inner map cannot be None.
User values for inner map cannot be None.
Validates MultiMapKey supplied to the function.
Validates MultiMapKey supplied to the function. Only MultiMapKey.MapEntry is accepted since functions are applied to Map's key-values only.
All registered function for a MultiMap.