=NULL && this is a null, without data type release x x=NULL && this is a Logical NULL x='' && this is a empty string x=NULL && now x is a null string ? VARTYPE(m.x,.T.),TYPE('m.x') ? VARTYPE(m.x) && return 'X', but it is a trick * in fact ? NULL+1 && return a null value ? m.x+1 && fire a error because you cannot concat a null string with a numberFabio