check for both arguments NULL on strings_differ
check for both arguments NULL on strings_differ

stapelberg/i3,stapelberg/i3,stapelberg/i3,i3/i3,stapelberg/i3,Airblader/i3,i3/i3,Airblader/i3,i3/i3,i3/i3,Airblader/i3,Airblader/i3