How can I count mber of empty fields in a record?

To count the mber of empty fields in a record:

/*Put all the fields to check if those are blank, You can also create a custom label OR custom setting */
Set fields = new Set{'Amount','Stagename'};
Integer counter = 0;
Map oppCounterMap = new Map();
for (Opportunity myOpp: Trigger.new) {
    for(String fieldName : fields){
        // Check if the field is Blank
        if(myOpp.get(fieldName) != null)
        counter++;
    }
    /*Map of Opportunity and the number of fields which are blank on the 
      respective Object */
    oppCounterMap.put(myOpp.Id, counter);
    counter= 0;
}