Nullability of reference types in type of parameter 'sender' of 'void Program.RefreshIconTimer_Tick(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.OnlineCalendarItemClickEvent(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.HolidayItemClickEvent(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.QuitItemClickEvent(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.TrayIcon_Click(object sender, MouseEventArgs e)' doesn't match the target delegate 'MouseEventHandler' (possibly because of nullability attributes).

Non-nullable field 'RefreshIconTimer' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Non-nullable field 'CalendarWeekNotifyIcon' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Nullability of reference types in type of parameter 'sender' of 'void Program.RefreshIconTimer_Tick(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.OnlineCalendarItemClickEvent(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.HolidayItemClickEvent(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.RefreshIconTimer_Tick(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.OnlineCalendarItemClickEvent(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.HolidayItemClickEvent(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.QuitItemClickEvent(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void Program.TrayIcon_Click(object sender, MouseEventArgs e)' doesn't match the target delegate 'MouseEventHandler' (possibly because of nullability attributes).

Non-nullable field 'RefreshIconTimer' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.