Make nullable parameters explicity nullable for PHP 8.4

[emteknetnz]

Implicitly nullable parameter types are deprecated in PHP 8.4

https://www.php.net/manual/it/migration84.deprecated.php#migration84.deprecated.core.implicitly-nullable-parameter

[k00ni]

I could be wrong, but changes regarding PHP 8 are currently collected in the php8 branch. Further more information about this are here: https://github.com/lanthaler/JsonLD/pull/107#issuecomment-1262015707

[emteknetnz]

Have updated PR to merge into the php8 branch

[mingalevme]

Quick workaround while PR is not merged:

composer req 'ml/json-ld:dev-php8#f87ba28e38f0bd14edf338fa5cf5529e6ed99cf8 as 1.3'

[k00ni]

Ping @lanthaler

[lanthaler]

Thanks and sorry for the delay on this