How to add description for argument without giving a default value?

[dbs4261]

As the title says, how do I add a description for a function parameter without giving that parameter a default value?
To name an argument, I can use either pybind11::arg or pybind11::arg_v. The constructor for pybind11::arg only takes a const char* name argument. Whereas the pybind11::arg_v constructor takes const char* name, T&& x, const char* descr. There is no constructor that can take const char* name, const char* descr without also providing a default argument. Is there a value that I can pass that signals there is no default value given?