Fix implicit nullable #481

Job	Run time
Quality control	49s
Linter	1m 25s
Security checks	18s
Unit tests, PHP ${{ matrix.php-versions }}, ${{ matrix.operating-system }}	0s
Unit tests, PHP ${{ matrix.php-versions }}, ${{ matrix.operating-system }}	-1s
Code coverage	-1s
Cleanup artifacts	-1s
	2m 29s

Provide feedback