Fixed string exif value corner case exception

src/ImageSharp/Metadata/Profiles/Exif/ExifEncodedStringHelpers.cs

@@ -80,7 +80,15 @@ public static int Write(EncodedString encodedString, Span<byte> destination)
         }
 
         public static unsafe int Write(Encoding encoding, string value, Span<byte> destination)
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER || NET
+            => encoding.GetBytes(value.AsSpan(), destination);
+#else
         {
+            if (value.Length == 0)
+            {
+                return 0;
+            }
+
             fixed (char* c = value)
             {
                 fixed (byte* b = destination)
@@ -89,6 +97,7 @@ public static unsafe int Write(Encoding encoding, string value, Span<byte> desti
                 }
             }
         }
+#endif
 
         private static bool TryDetect(ReadOnlySpan<byte> buffer, out CharacterCode code)
         {

tests/ImageSharp.Tests/Formats/Jpg/JpegEncoderTests.Metadata.cs

@@ -0,0 +1,33 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.IO;
+using SixLabors.ImageSharp.Formats.Jpeg;
+using SixLabors.ImageSharp.PixelFormats;
+
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Jpg
+{
+    [Trait("Format", "Jpg")]
+    public partial class JpegEncoderTests
+    {
+        [Theory]
+        [WithFile(TestImages.Jpeg.Issues.ValidExifArgumentNullExceptionOnEncode, PixelTypes.Rgba32)]
+        public void Encode_WithValidExifProfile_DoesNotThrowException<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            Exception ex = Record.Exception(() =>
+            {
+                var encoder = new JpegEncoder();
+                var stream = new MemoryStream();
+
+                using Image<TPixel> image = provider.GetImage(JpegDecoder);
+                image.Save(stream, encoder);
+            });
+
+            Assert.Null(ex);
+        }
+    }
+}

tests/ImageSharp.Tests/Formats/Jpg/JpegEncoderTests.cs

@@ -20,7 +20,7 @@
 namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 {
     [Trait("Format", "Jpg")]
-    public class JpegEncoderTests
+    public partial class JpegEncoderTests
     {
         private static JpegEncoder JpegEncoder => new();
 

tests/ImageSharp.Tests/TestImages.cs

@@ -264,6 +264,7 @@ public static class Issues
                 public const string InvalidIptcTag = "Jpg/issues/Issue1942InvalidIptcTag.jpg";
                 public const string Issue2057App1Parsing = "Jpg/issues/Issue2057-App1Parsing.jpg";
                 public const string ExifNullArrayTag = "Jpg/issues/issue-2056-exif-null-array.jpg";
+                public const string ValidExifArgumentNullExceptionOnEncode = "Jpg/issues/Issue2087-exif-null-reference-on-encode.jpg";
 
                 public static class Fuzz
                 {