feat: remove more warnings.

src/Ursa/Controls/DateTimePicker/CalendarView.cs

@@ -260,10 +260,7 @@ public class CalendarView : TemplatedControl
             ContextDate = ContextDate.With(startYear: range.start, endYear: range.end);
             _dateContextSyncing = false;
             UpdateYearButtons();
-            return;
         }
-
-        if (Mode == CalendarViewMode.Century) return;
     }
 
     /// <summary>

src/Ursa/Controls/DateTimePicker/DateRangePicker.cs

@@ -310,7 +310,7 @@ public class DateRangePicker : DatePickerBase, IClearControl
 
     private void OnTextChangedInternal(TextBox? textBox, AvaloniaProperty property, bool fromText = false)
     {
-        if (string.IsNullOrEmpty(textBox?.Text))
+        if (textBox?.Text is null || string.IsNullOrEmpty(textBox.Text))
         {
             SetCurrentValue(property, null);
             _startCalendar?.ClearSelection();