return null;
}
@Override
public boolean isOccupiedByExecutionCourse(final ExecutionCourse executionCourse, final DateTime start, final DateTime end) {
final Lesson lesson = getLesson();
if (lesson.getExecutionCourse() == executionCourse) {
final List<Interval> intervals =
getEventSpaceOccupationIntervals(start.toYearMonthDay(), end.toYearMonthDay().plusDays(1));
for (final Interval interval : intervals) {
if (start.isBefore(interval.getEnd()) && end.isAfter(interval.getStart())) {
return true;