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
Merge branch 'step-9' into step-10
Merge branch 'step-10' into step-11
Merge branch 'step-11' into step-12
Merge branch 'step-12' into step-13
Merge branch 'step-13' into step-14
Merge branch 'step-14' into step-15