Add missing final
Merge branch 'step-2' into step-3
Merge branch 'step-3' into step-4
Merge branch 'step-4' into step-5
Merge branch 'step-5' into step-6
Merge branch 'step-6' into step-7
Merge branch 'step-7' into step-8
Upgrade rubycollect4j
Merge branch 'step-8' into step-9