tools/minify-js: Improve type checking.
tools/minify-js: Improve type checking.

* Use Optional where needed.
* Add type to variables because otherwise it'll be Any.

rht/zulip,tommyip/zulip,brainwane/zulip,tommyip/zulip,hackerkid/zulip,jackrzhang/zulip,synicalsyntax/zulip,dhcrzf/zulip,jrowan/zulip,christi3k/zulip,vabs22/zulip,kou/zulip,verma-varsha/zulip,shubhamdhama/zulip,christi3k/zulip,zulip/zulip,mahim97/zulip,Galexrt/zulip,brockwhittaker/zulip,zulip/zulip,zulip/zulip,mahim97/zulip,eeshangarg/zulip,brainwane/zulip,shubhamdhama/zulip,eeshangarg/zulip,christi3k/zulip,amanharitsh123/zulip,rht/zulip,dhcrzf/zulip,Galexrt/zulip,synicalsyntax/zulip,brockwhittaker/zulip,vaidap/zulip,jrowan/zulip,timabbott/zulip,rishig/zulip,rishig/zulip,timabbott/zulip,punchagan/zulip,zulip/zulip,punchagan/zulip,brockwhittaker/zulip,rishig/zulip,hackerkid/zulip,vaidap/zulip,andersk/zulip,tommyip/zulip,punchagan/zulip,hackerkid/zulip,christi3k/zulip,andersk/zulip,amanharitsh123/zulip,rishig/zulip,mahim97/zulip,Galexrt/zulip,timabbott/zulip,synicalsyntax/zulip,dhcrzf/zulip,rht/zulip,punchagan/zulip,dhcrzf/zulip,andersk/zulip,jackrzhang/zulip,Galexrt/zulip,jackrzhang/zulip,timabbott/zulip,vaidap/zulip,brainwane/zulip,eeshangarg/zulip,synicalsyntax/zulip,shubhamdhama/zulip,vabs22/zulip,jrowan/zulip,hackerkid/zulip,kou/zulip,brockwhittaker/zulip,timabbott/zulip,eeshangarg/zulip,vabs22/zulip,hackerkid/zulip,andersk/zulip,j831/zulip,amanharitsh123/zulip,andersk/zulip,brainwane/zulip,kou/zulip,jackrzhang/zulip,Galexrt/zulip,eeshangarg/zulip,synicalsyntax/zulip,mahim97/zulip,showell/zulip,jackrzhang/zulip,showell/zulip,verma-varsha/zulip,zulip/zulip,rishig/zulip,mahim97/zulip,punchagan/zulip,brainwane/zulip,j831/zulip,jackrzhang/zulip,vabs22/zulip,rishig/zulip,dhcrzf/zulip,timabbott/zulip,shubhamdhama/zulip,showell/zulip,vabs22/zulip,vaidap/zulip,vaidap/zulip,kou/zulip,j831/zulip,punchagan/zulip,Galexrt/zulip,j831/zulip,andersk/zulip,shubhamdhama/zulip,eeshangarg/zulip,brockwhittaker/zulip,showell/zulip,kou/zulip,dhcrzf/zulip,shubhamdhama/zulip,jrowan/zulip,christi3k/zulip,tommyip/zulip,kou/zulip,hackerkid/zulip,showell/zulip,mahim97/zulip,verma-varsha/zulip,rht/zulip,andersk/zulip,tommyip/zulip,timabbott/zulip,rht/zulip,brainwane/zulip,zulip/zulip,vabs22/zulip,rht/zulip,jackrzhang/zulip,eeshangarg/zulip,amanharitsh123/zulip,j831/zulip,zulip/zulip,christi3k/zulip,punchagan/zulip,rht/zulip,brockwhittaker/zulip,dhcrzf/zulip,showell/zulip,amanharitsh123/zulip,showell/zulip,rishig/zulip,jrowan/zulip,Galexrt/zulip,verma-varsha/zulip,hackerkid/zulip,vaidap/zulip,brainwane/zulip,tommyip/zulip,verma-varsha/zulip,amanharitsh123/zulip,kou/zulip,jrowan/zulip,synicalsyntax/zulip,synicalsyntax/zulip,verma-varsha/zulip,j831/zulip,tommyip/zulip,shubhamdhama/zulip