8231921: (se) SelectorImpl.register does not need to set the attachment when it is null
Reviewed-by: bpb
^build/
^dist/
^.idea/
nbproject/private/
^webrev
^.src-rev$
^.jib/
(^|/)\.DS_Store
(^|/)\.metadata/
(^|/)\.recommenders/
test/nashorn/script/external
test/nashorn/lib
NashornProfile.txt
(^|/)JTreport/
(^|/)JTwork/
(^|/)\.git/
^src/utils/hsdis/build/