Make argument of NullType constructor nullable
Make argument of NullType constructor nullable

frida/vala,spidermonkdust/vala,themiwi/vala,flobrosch/vala-fixes,severinh/vala,kamanashisroy/aroop,rvu95/vala,playya/vala,GNOME/vala,GNOME/vala,xdave/pvala,playya/vala,tjol/vala-tjol,Distrotech/vala,playya/vala,frida/vala,flobrosch/vala-fixes,themiwi/vala,Distrotech/vala,severinh/vala,tjol/vala-tjol,severinh/vala,GNOME/vala,rvu95/vala,frida/vala,rvu95/vala,spidermonkdust/vala,tjol/vala-tjol,jessevdk/vala,flobrosch/vala-fixes,GNOME/vala,spidermonkdust/vala,jessevdk/vala,themiwi/vala,frida/vala,Distrotech/vala,frida/vala,jessevdk/vala,kamanashisroy/aroop,kamanashisroy/aroop