code: func (args Args) UniqueExactMatch(key, source string) bool {
  	fieldValues := args.fields[key]
  	//do not filter if there is no filter set or cannot determine filter
  	if len(fieldValues) == 0 {
  		return true
  	}
  	if len(args.fields[key]) != 1 {
  		return false
  	}
  
  	// try to match full name value to avoid O(N) regular expression matching
  	return fieldValues[source]
  }
docs: // UniqueExactMatch returns true if there is only one value and the source
  // matches exactly the value.