Make CodeIgniter::context nullable to handle access before initialization

[samsonasik]

@kenjis this is to handle context is accessed before initialized as decribed at #5650 (comment) on composer update && php spark serve, tested in php 8.1

php builds development
composer update
php spark serve

Before

CodeIgniter v4.1.8 Command Line Tool - Server Time: 2022-02-18 17:42:23 UTC-06:00

An uncaught Exception was encountered

Type:        Error
Message:     Typed property CodeIgniter\CodeIgniter::$context must not be accessed before initialization
Filename:    /Users/samsonasik/www/ci4-prj/vendor/codeigniter4/codeigniter4/system/CodeIgniter.php
Line Number: 308

        Backtrace:
                                                -48 - /Users/samsonasik/www/ci4-prj/vendor/codeigniter4/codeigniter4/system/CLI/Console.php::run
                                                                -57 - /Users/samsonasik/www/ci4-prj/spark::run

After

CodeIgniter v4.1.8 Command Line Tool - Server Time: 2022-02-18 17:47:40 UTC-06:00

An uncaught Exception was encountered

Type:        AssertionError
Message:     Context must be set before run() is called. If you are upgrading from 4.1.x, you need to merge `public/index.php` and `spark` file from `vendor/codeigniter4/framework`.
Filename:    /Users/samsonasik/www/ci4-prj/vendor/codeigniter4/codeigniter4/system/CodeIgniter.php
Line Number: 309

        Backtrace:
                                                -309 - /Users/samsonasik/www/ci4-prj/vendor/codeigniter4/codeigniter4/system/CodeIgniter.php::assert
                                                                -48 - /Users/samsonasik/www/ci4-prj/vendor/codeigniter4/codeigniter4/system/CLI/Console.php::run
                                                                -57 - /Users/samsonasik/www/ci4-prj/spark::run

Checklist:

• Securely signed commits

[samsonasik]

@kenjis here is the proof:

without initialization, got A::$context must not be accessed before initialization : https://3v4l.org/3afAK
with initialization, got Context must be set before run() is called : https://3v4l.org/DFddo

[samsonasik]

I am merging early so user that uses develop version can immediately see the clue in the error message.

[kenjis]

@samsonasik Thank you!

[MGatner]

Thanks for the quick turnaround on this one.