...
On Expression tab
function main() {
if (isNull(V1)) {
return 12;
} else {
var myMonth = V1.getMonth();
return myMonth;
}
}
On the Pick List tab
List months 0 to 11 12 (e.g., 0 = January, etc.; 12 = "Missing Date")
Exclude Previous Years Approach
Modify the picklist options to include: 12 = Previous year, 13 = Missing date
function main() {
if(isNull(v1)) { return 13;
} else {
var myMonth = V1.getMonth();
var myYear = V1.getYear();
if (myYear <= 2015) { // previous year = 2015, replace as appropriate
return 12;
} else {
return myMonth;
}
}
}