code: public int get(DateTimeFieldType fieldType) {
          if (fieldType == null) {
              throw new IllegalArgumentException("The DateTimeFieldType must not be null");
          }
          if (isSupported(fieldType) == false) {
              throw new IllegalArgumentException("Field '" + fieldType + "' is not supported");
          }
          return fieldType.getField(getChronology()).get(getLocalMillis());
      }
docs: Get the value of one of the fields of a datetime.
  <p>
  This method gets the value of the specified field.
  For example:
  <pre>
  LocalDate dt = LocalDate.nowDefaultZone();
  int year = dt.get(DateTimeFieldType.year());
  </pre>
  
  @param fieldType  a field type, usually obtained from DateTimeFieldType, not null
  @return the value of that field
  @throws IllegalArgumentException if the field type is null or unsupported