if (acAcademicYearsField == null) {
acAcademicYearsField = new AcademicYearsDurationField(this);
acAcademicYear = new AcademicYearDateTimeField(this);
acAcademicTrimester = new AcademicTrimesterDateTimeField(this);
acAcademicTrimestersField = new AcademicTrimesterDurationField(this);
acAcademicSemester = new AcademicSemesterDateTimeField(this);
acAcademicSemestersField = new AcademicSemestersDurationField(this);
acAcademicSemesterOfAcademicYear = new AcademicSemesterOfAcademicYearDateTimeField(this);
acDayOfAcademicSemester = new DayOfAcademicSemesterDateTimeField(this);