edit-event.ts

    // Form variables.
    descriptionControl: FormControl<string>;
    form!: FormGroup<{
        name: FormControl<string>;
        timestart: FormControl<string>;
        eventtype: FormControl<AddonCalendarEventType | null>;
        categoryid: FormControl<number | null>;
        courseid: FormControl<number>;
        groupcourseid: FormControl<number | null>;
        groupid: FormControl<number | null>;
        description: FormControl<string>;
        location: FormControl<string>;
        duration: FormControl<number>;
        timedurationuntil: FormControl<string>;
        timedurationminutes: FormControl<number | null>;
        repeat: FormControl<boolean>;
        repeats: FormControl<number>;
        repeateditall: FormControl<number>;
    }>;
      
      // Remove all form init logic from constructor and ngOnInit, and put this instead in ngOnInit:
      
      this.form = new FormGroup({
            name: new FormControl('', { validators: Validators.required, nonNullable: true }),
            timestart: new FormControl(currentDate, { validators: Validators.required, nonNullable: true }),
            eventtype: new FormControl<AddonCalendarEventType | null>(null, Validators.required),
            categoryid: new FormControl<number | null>(null),
            courseid: new FormControl(this.courseId, { nonNullable: true }),
            groupcourseid: new FormControl<number | null>(null),
            groupid: new FormControl<number | null>(null),
            description: this.descriptionControl,
            location: new FormControl('', { nonNullable: true }),
            duration: new FormControl(0, { nonNullable: true }),
            timedurationuntil: new FormControl(currentDate, { nonNullable: true }),
            timedurationminutes: new FormControl<number | null>(null),
            repeat: new FormControl(false, { nonNullable: true }),
            repeats: new FormControl(1, { nonNullable: true }),
            repeateditall: new FormControl(1, { nonNullable: true }),
        });