codegen: Fix transform_value result when target_type is null
codegen: Fix transform_value result when target_type is null

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