Revert "Remove NULL check in favour of __ws_nonnull__ macro"

This reverts commit a2d02e14352ebba41f5cc0e68ba8814d1ef10db9.
Revert "Fix: Use __ws_nonnull__ instead of NULL runtime check"

This reverts commit ffae3a841fe5e77bc1863adc789996068e8b6660.