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));
}