public MapperAction <TContext> GetMapper(Type fromType, Type toType)
        {
            var toNullableType = toType.GetGenericArguments()[0];

            _mapper.RequireOneWayMap(fromType, toNullableType, "MapNonNullableToNullable");
            var nonNullToNullMapper = _mapper.GetMapper(fromType, toNullableType);

            return((from, to, context) => nonNullToNullMapper.MapObject(from, to, context));
        }