add meaningful error message
add meaningful error message

nicolaasmatthijs/Hilary,mrvisser/Hilary,ExC0d3/Hilary,jfederico/Hilary,jfederico/Hilary,simong/Hilary,ExC0d3/Hilary,mrvisser/Hilary,Orodan/Hilary,timdegroote/Hilary,Orodan/Hilary,simong/Hilary,stuartf/Hilary,timdegroote/Hilary,nicolaasmatthijs/Hilary,stuartf/Hilary