docs: protected void assemble(Fields fields) {
          if (getBase() == null) {
              super.assemble(fields);
  
              // Coptic, like Julian, has no year zero.
              fields.year = new SkipDateTimeField(this, fields.year);
              fields.weekyear = new SkipDateTimeField(this, fields.weekyear);
              
              fields.era = ERA_FIELD;
              fields.monthOfYear = new BasicMonthOfYearDateTimeField(this, 13);
              fields.months = fields.monthOfYear.getDurationField();
          }
      }