Added extra checks to the ExifReader (fixes #175).

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

@@ -73,6 +73,8 @@ namespace ImageSharp
         /// </returns>
         public Collection<ExifValue> Read(byte[] data)
         {
+            DebugGuard.NotNull(data, nameof(data));
+
             Collection<ExifValue> result = new Collection<ExifValue>();
 
             this.exifData = data;
@@ -390,7 +392,13 @@ namespace ImageSharp
 
         private string GetString(uint length)
         {
-            return ToString(this.GetBytes(length));
+            byte[] data = this.GetBytes(length);
+            if (data == null || data.Length == 0)
+            {
+                return null;
+            }
+
+            return ToString(data);
         }
 
         private void GetThumbnail(uint offset)

tests/ImageSharp.Tests/MetaData/Profiles/Exif/ExifReaderTests.cs

@@ -0,0 +1,35 @@
+// <copyright file="ExifReaderTests.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Tests
+{
+    using System.Collections.ObjectModel;
+    using Xunit;
+
+    public class ExifReaderTests
+    {
+        [Fact]
+        public void Read_DataIsEmpty_ReturnsEmptyCollection()
+        {
+            ExifReader reader = new ExifReader();
+            byte[] data = new byte[] { };
+
+            Collection<ExifValue> result = reader.Read(data);
+
+            Assert.Equal(0, result.Count);
+        }
+
+        [Fact]
+        public void Read_DataIsMinimal_ReturnsEmptyCollection()
+        {
+            ExifReader reader = new ExifReader();
+            byte[] data = new byte[] { 69, 120, 105, 102, 0, 0 };
+
+            Collection<ExifValue> result = reader.Read(data);
+
+            Assert.Equal(0, result.Count);
+        }
+    }
+}