diff --git a/Converters/StringToImageConverter.cs b/Converters/StringToImageConverter.cs
index b595589..cff9f48 100644
--- a/Converters/StringToImageConverter.cs
+++ b/Converters/StringToImageConverter.cs
@@ -8,7 +8,7 @@ namespace SunlightAggregationTerminal.Converters
 {
     public class StringToImageConverter: IValueConverter
     {
-        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
         {
             if (value !=null)
             {
@@ -29,7 +29,7 @@ namespace SunlightAggregationTerminal.Converters
             return ImageSource.FromFile("sunlightlogo.png");
         }
 
-        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
         {
             // 通常图片转回字符串在 UI 上很少用到，可以抛出异常或留空
             throw new NotImplementedException();