PHPStan level 9 failure

[Ndiritu]

PHP version: 7.4

Description
Running PHPStan level 9 checks on this library fails with

 ------ -----------------------------------------------------------------------------------------------
  Line   FulfilledPromise.php
 ------ -----------------------------------------------------------------------------------------------
  58     Method Http\Promise\FulfilledPromise::wait() should return T but return statement is missing.
 ------ -----------------------------------------------------------------------------------------------

 ------ ----------------------------------------------------------------------------------------------
  Line   RejectedPromise.php
 ------ ----------------------------------------------------------------------------------------------
  55     Method Http\Promise\RejectedPromise::wait() should return T but return statement is missing.
 ------ ----------------------------------------------------------------------------------------------


 [ERROR] Found 2 errors

How to reproduce
phpstan analyze --level 9 src/

Possible Solution
Expand return type of wait() to accommodate void and null return types