Ensure exifData is set

src/ImageSharp/MetaData/Profiles/Exif/ExifReader.cs

@@ -27,9 +27,7 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Exif
 
         public ExifReader(byte[] exifData)
         {
-            DebugGuard.NotNull(exifData, nameof(exifData));
+            this.exifData = exifData ?? throw new ArgumentNullException(nameof(exifData));
-
-            this.exifData = exifData;
         }
 
         private delegate TDataType ConverterMethod<TDataType>(ReadOnlySpan<byte> data);