std:optional question

Hello the list,

sorry it's a noob question ...

how to deal with a c++ function with a signature including a 
std::optional parameter for python?

i saw that
https://stackoverflow.com/questions/66530923/swig-python-wrapper-for-stdoptional

and
https://gist.github.com/vadz/44bcb03ea2ca8a370012a1f47aa00eaf

but not sure how to proceed.

i put

%typemap(in) std::optional<std::string> %{
   if ($input == Py_None) {
     $1 = std::optional<std::string>();
   } else {
     $1 = std::optional<std::string>(PyString_AsString($input));
   }
%}
in my .i file

but i encounter the error

TypeError: Wrong number or type of arguments for overloaded function 
'say_msg'.
   Possible C/C++ prototypes are:
     say_msg(std::string,std::optional< string >)
     say_msg(std::string)

my function is for example

void say_msg(std::string name, std::optional<string> msg = std::nullopt);


do i need a typecheck as
https://www.swig.org/Doc4.1/Typemaps.html#Typemaps_nn27

but can t find a good SWIG_TYPECHECK_XXX candidate

thanks for your advices