8209087: Clean up runtime code that compares 'this' to NULL
Summary: Remove 'this' to NULL comparisons from methods and check if calling objects of these methods could be NULL.
Reviewed-by: lfoltan, gziemski
^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/.*