can't get call_if to work because of etl::optional

[KammutierSpule]

while using delegate call_if, I got this error:

error: cannot convert 'etl::enable_if_t<true, etl::optional<esp_modem::command_result> >' {aka 'etl::optional<esp_modem::command_result>'} to 'esp_modem::command_result' in return

should it work? if I call the delegate directly it works.