Fixing some @Nullable inconsistencies in shell/
Fixing some @Nullable inconsistencies in shell/

Summary: Fixing some @Nullable inconsistencies and documenting some implicit assumptions using Preconditions.checkNotNull

Test Plan: buck test --all

illicitonion/buck,rowillia/buck,clonetwin26/buck,grumpyjames/buck,romanoid/buck,illicitonion/buck,Dominator008/buck,zpao/buck,rhencke/buck,rowillia/buck,mogers/buck,liuyang-li/buck,illicitonion/buck,vschs007/buck,sdwilsh/buck,mikekap/buck,1yvT0s/buck,Dominator008/buck,siddhartharay007/buck,luiseduardohdbackup/buck,zhuxiaohao/buck,mikekap/buck,artiya4u/buck,facebook/buck,kageiit/buck,neonichu/buck,robbertvanginkel/buck,vine/buck,Heart2009/buck,SeleniumHQ/buck,liuyang-li/buck,davido/buck,zhan-xiong/buck,darkforestzero/buck,daedric/buck,hgl888/buck,vine/buck,luiseduardohdbackup/buck,1yvT0s/buck,Heart2009/buck,Heart2009/buck,rowillia/buck,dushmis/buck,JoelMarcey/buck,rhencke/buck,darkforestzero/buck,k21/buck,1yvT0s/buck,Dominator008/buck,vschs007/buck,sdwilsh/buck,stuhood/buck,nguyentruongtho/buck,shybovycha/buck,liuyang-li/buck,rmaz/buck,shybovycha/buck,neonichu/buck,grumpyjames/buck,marcinkwiatkowski/buck,dsyang/buck,robbertvanginkel/buck,janicduplessis/buck,janicduplessis/buck,liuyang-li/buck,LegNeato/buck,justinmuller/buck,liuyang-li/buck,k21/buck,clonetwin26/buck,JoelMarcey/buck,tgummerer/buck,zhuxiaohao/buck,marcinkwiatkowski/buck,Distrotech/buck,shybovycha/buck,JoelMarcey/buck,Learn-Android-app/buck,zhan-xiong/buck,zpao/buck,facebook/buck,JoelMarcey/buck,bocon13/buck,shs96c/buck,shs96c/buck,janicduplessis/buck,dsyang/buck,davido/buck,liuyang-li/buck,clonetwin26/buck,clonetwin26/buck,illicitonion/buck,sdwilsh/buck,Distrotech/buck,mogers/buck,neonichu/buck,Dominator008/buck,artiya4u/buck,robbertvanginkel/buck,davido/buck,1yvT0s/buck,kageiit/buck,justinmuller/buck,tgummerer/buck,rmaz/buck,Learn-Android-app/buck,k21/buck,daedric/buck,OkBuilds/buck,justinmuller/buck,hgl888/buck,OkBuilds/buck,Distrotech/buck,tgummerer/buck,luiseduardohdbackup/buck,SeleniumHQ/buck,artiya4u/buck,JoelMarcey/buck,sdwilsh/buck,romanoid/buck,liuyang-li/buck,janicduplessis/buck,raviagarwal7/buck,kageiit/buck,sdwilsh/buck,raviagarwal7/buck,MarkRunWu/buck,robbertvanginkel/buck,siddhartharay007/buck,bocon13/buck,Distrotech/buck,mogers/buck,rmaz/buck,vschs007/buck,Addepar/buck,brettwooldridge/buck,tgummerer/buck,tgummerer/buck,vschs007/buck,daedric/buck,dpursehouse/buck,zhan-xiong/buck,shybovycha/buck,brettwooldridge/buck,mread/buck,pwz3n0/buck,shs96c/buck,shybovycha/buck,OkBuilds/buck,shybovycha/buck,vine/buck,vschs007/buck,shs96c/buck,daedric/buck,MarkRunWu/buck,mikekap/buck,hgl888/buck,ilya-klyuchnikov/buck,sdwilsh/buck,zhuxiaohao/buck,1yvT0s/buck,artiya4u/buck,rmaz/buck,justinmuller/buck,robbertvanginkel/buck,hgl888/buck,SeleniumHQ/buck,davido/buck,ilya-klyuchnikov/buck,sdwilsh/buck,zhan-xiong/buck,dsyang/buck,daedric/buck,mikekap/buck,Heart2009/buck,mogers/buck,mogers/buck,shs96c/buck,zhuxiaohao/buck,Learn-Android-app/buck,bocon13/buck,mogers/buck,shs96c/buck,hgl888/buck,SeleniumHQ/buck,marcinkwiatkowski/buck,illicitonion/buck,dsyang/buck,daedric/buck,lukw00/buck,Addepar/buck,mread/buck,dsyang/buck,ilya-klyuchnikov/buck,k21/buck,zpao/buck,rhencke/buck,pwz3n0/buck,daedric/buck,vine/buck,OkBuilds/buck,lukw00/buck,pwz3n0/buck,siddhartharay007/buck,nguyentruongtho/buck,rmaz/buck,stuhood/buck,dpursehouse/buck,Learn-Android-app/buck,stuhood/buck,Addepar/buck,grumpyjames/buck,stuhood/buck,OkBuilds/buck,romanoid/buck,LegNeato/buck,Addepar/buck,pwz3n0/buck,illicitonion/buck,zhan-xiong/buck,JoelMarcey/buck,darkforestzero/buck,SeleniumHQ/buck,stuhood/buck,zpao/buck,lukw00/buck,grumpyjames/buck,LegNeato/buck,dushmis/buck,romanoid/buck,SeleniumHQ/buck,artiya4u/buck,clonetwin26/buck,bocon13/buck,lukw00/buck,artiya4u/buck,clonetwin26/buck,nguyentruongtho/buck,dsyang/buck,vschs007/buck,hgl888/buck,Heart2009/buck,mnuessler/buck,tgummerer/buck,sdwilsh/buck,luiseduardohdbackup/buck,LegNeato/buck,brettwooldridge/buck,rowillia/buck,raviagarwal7/buck,darkforestzero/buck,romanoid/buck,Dominator008/buck,rmaz/buck,marcinkwiatkowski/buck,LegNeato/buck,liuyang-li/buck,marcinkwiatkowski/buck,darkforestzero/buck,rmaz/buck,illicitonion/buck,bocon13/buck,shybovycha/buck,kageiit/buck,justinmuller/buck,dsyang/buck,artiya4u/buck,mogers/buck,dsyang/buck,mogers/buck,dsyang/buck,rhencke/buck,mikekap/buck,liuyang-li/buck,dsyang/buck,illicitonion/buck,OkBuilds/buck,marcinkwiatkowski/buck,Addepar/buck,brettwooldridge/buck,Dominator008/buck,Distrotech/buck,darkforestzero/buck,artiya4u/buck,pwz3n0/buck,zhan-xiong/buck,grumpyjames/buck,shs96c/buck,OkBuilds/buck,ilya-klyuchnikov/buck,vine/buck,davido/buck,marcinkwiatkowski/buck,mread/buck,rmaz/buck,Dominator008/buck,siddhartharay007/buck,luiseduardohdbackup/buck,vschs007/buck,facebook/buck,janicduplessis/buck,bocon13/buck,shs96c/buck,neonichu/buck,shs96c/buck,zhan-xiong/buck,Distrotech/buck,mread/buck,romanoid/buck,bocon13/buck,sdwilsh/buck,rowillia/buck,Learn-Android-app/buck,vine/buck,vine/buck,JoelMarcey/buck,Distrotech/buck,janicduplessis/buck,rmaz/buck,LegNeato/buck,Learn-Android-app/buck,lukw00/buck,zhan-xiong/buck,stuhood/buck,Dominator008/buck,raviagarwal7/buck,SeleniumHQ/buck,daedric/buck,Learn-Android-app/buck,zhuxiaohao/buck,rmaz/buck,marcinkwiatkowski/buck,dsyang/buck,shybovycha/buck,SeleniumHQ/buck,tgummerer/buck,shs96c/buck,mnuessler/buck,Addepar/buck,illicitonion/buck,bocon13/buck,1yvT0s/buck,SeleniumHQ/buck,tgummerer/buck,zhan-xiong/buck,LegNeato/buck,siddhartharay007/buck,raviagarwal7/buck,rowillia/buck,rmaz/buck,grumpyjames/buck,pwz3n0/buck,shs96c/buck,ilya-klyuchnikov/buck,k21/buck,shybovycha/buck,mogers/buck,lukw00/buck,Distrotech/buck,1yvT0s/buck,rhencke/buck,Learn-Android-app/buck,JoelMarcey/buck,zhan-xiong/buck,brettwooldridge/buck,mogers/buck,davido/buck,zhuxiaohao/buck,romanoid/buck,janicduplessis/buck,Dominator008/buck,stuhood/buck,davido/buck,JoelMarcey/buck,justinmuller/buck,grumpyjames/buck,luiseduardohdbackup/buck,rhencke/buck,dushmis/buck,1yvT0s/buck,raviagarwal7/buck,neonichu/buck,davido/buck,k21/buck,pwz3n0/buck,rowillia/buck,hgl888/buck,clonetwin26/buck,pwz3n0/buck,grumpyjames/buck,LegNeato/buck,dsyang/buck,nguyentruongtho/buck,mikekap/buck,SeleniumHQ/buck,rhencke/buck,zpao/buck,justinmuller/buck,marcinkwiatkowski/buck,grumpyjames/buck,zhuxiaohao/buck,siddhartharay007/buck,Dominator008/buck,dpursehouse/buck,k21/buck,zhan-xiong/buck,luiseduardohdbackup/buck,MarkRunWu/buck,nguyentruongtho/buck,romanoid/buck,tgummerer/buck,neonichu/buck,k21/buck,dushmis/buck,daedric/buck,clonetwin26/buck,stuhood/buck,mnuessler/buck,mikekap/buck,nguyentruongtho/buck,Heart2009/buck,SeleniumHQ/buck,bocon13/buck,kageiit/buck,davido/buck,marcinkwiatkowski/buck,vine/buck,mnuessler/buck,vine/buck,clonetwin26/buck,Addepar/buck,shs96c/buck,Addepar/buck,lukw00/buck,mnuessler/buck,clonetwin26/buck,justinmuller/buck,darkforestzero/buck,dpursehouse/buck,JoelMarcey/buck,ilya-klyuchnikov/buck,zhuxiaohao/buck,janicduplessis/buck,dpursehouse/buck,neonichu/buck,lukw00/buck,raviagarwal7/buck,romanoid/buck,Addepar/buck,OkBuilds/buck,pwz3n0/buck,kageiit/buck,shybovycha/buck,darkforestzero/buck,brettwooldridge/buck,mnuessler/buck,grumpyjames/buck,raviagarwal7/buck,ilya-klyuchnikov/buck,vine/buck,sdwilsh/buck,mikekap/buck,justinmuller/buck,brettwooldridge/buck,mikekap/buck,shybovycha/buck,romanoid/buck,hgl888/buck,shybovycha/buck,raviagarwal7/buck,marcinkwiatkowski/buck,davido/buck,rowillia/buck,LegNeato/buck,k21/buck,vschs007/buck,illicitonion/buck,sdwilsh/buck,rhencke/buck,romanoid/buck,rhencke/buck,rmaz/buck,justinmuller/buck,zhan-xiong/buck,zpao/buck,ilya-klyuchnikov/buck,LegNeato/buck,raviagarwal7/buck,robbertvanginkel/buck,artiya4u/buck,siddhartharay007/buck,MarkRunWu/buck,daedric/buck,pwz3n0/buck,dushmis/buck,sdwilsh/buck,janicduplessis/buck,OkBuilds/buck,janicduplessis/buck,daedric/buck,stuhood/buck,Learn-Android-app/buck,marcinkwiatkowski/buck,bocon13/buck,JoelMarcey/buck,romanoid/buck,OkBuilds/buck,vine/buck,dushmis/buck,rowillia/buck,vschs007/buck,daedric/buck,illicitonion/buck,Heart2009/buck,OkBuilds/buck,vschs007/buck,luiseduardohdbackup/buck,rhencke/buck,k21/buck,MarkRunWu/buck,shybovycha/buck,robbertvanginkel/buck,brettwooldridge/buck,raviagarwal7/buck,brettwooldridge/buck,JoelMarcey/buck,marcinkwiatkowski/buck,lukw00/buck,Heart2009/buck,zhuxiaohao/buck,darkforestzero/buck,pwz3n0/buck,SeleniumHQ/buck,kageiit/buck,rhencke/buck,daedric/buck,dushmis/buck,mnuessler/buck,ilya-klyuchnikov/buck,k21/buck,OkBuilds/buck,mikekap/buck,nguyentruongtho/buck,mread/buck,artiya4u/buck,hgl888/buck,shs96c/buck,1yvT0s/buck,Distrotech/buck,mogers/buck,robbertvanginkel/buck,romanoid/buck,Addepar/buck,darkforestzero/buck,facebook/buck,rowillia/buck,ilya-klyuchnikov/buck,liuyang-li/buck,tgummerer/buck,ilya-klyuchnikov/buck,mnuessler/buck,facebook/buck,lukw00/buck,robbertvanginkel/buck,robbertvanginkel/buck,Dominator008/buck,zpao/buck,Learn-Android-app/buck,MarkRunWu/buck,neonichu/buck,rowillia/buck,rowillia/buck,illicitonion/buck,LegNeato/buck,Distrotech/buck,dushmis/buck,sdwilsh/buck,dpursehouse/buck,grumpyjames/buck,raviagarwal7/buck,mnuessler/buck,robbertvanginkel/buck,zhan-xiong/buck,k21/buck,Dominator008/buck,illicitonion/buck,ilya-klyuchnikov/buck,justinmuller/buck,dushmis/buck,robbertvanginkel/buck,stuhood/buck,davido/buck,brettwooldridge/buck,davido/buck,vschs007/buck,tgummerer/buck,robbertvanginkel/buck,janicduplessis/buck,siddhartharay007/buck,SeleniumHQ/buck,bocon13/buck,facebook/buck,ilya-klyuchnikov/buck,clonetwin26/buck,brettwooldridge/buck,Addepar/buck,mikekap/buck,vschs007/buck,MarkRunWu/buck,brettwooldridge/buck,darkforestzero/buck,rmaz/buck,facebook/buck,Addepar/buck,liuyang-li/buck,Learn-Android-app/buck,brettwooldridge/buck,darkforestzero/buck,dpursehouse/buck,mikekap/buck,justinmuller/buck,bocon13/buck,grumpyjames/buck,luiseduardohdbackup/buck,mread/buck,LegNeato/buck,neonichu/buck,k21/buck,davido/buck,lukw00/buck,raviagarwal7/buck,MarkRunWu/buck,justinmuller/buck,clonetwin26/buck,dsyang/buck,janicduplessis/buck,Distrotech/buck,Addepar/buck,Heart2009/buck,vschs007/buck,artiya4u/buck,siddhartharay007/buck,darkforestzero/buck,dushmis/buck,LegNeato/buck,JoelMarcey/buck,stuhood/buck,clonetwin26/buck,dpursehouse/buck,OkBuilds/buck