8204152: SignedObject throws NullPointerException for null keys with an initialized Signature object
Summary: Check for null and throw InvalidKeyException to maintain same behavior
Reviewed-by: xuelei
^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/.*