From 771c739a90dd404c032a22d3943cbf85dad3008a Mon Sep 17 00:00:00 2001
From: JimBobSquarePants <james_south@hotmail.com>
Date: Fri, 25 Aug 2017 13:54:38 +1000
Subject: [PATCH] Fix png decode span bug on Core 2.0

---
 src/ImageSharp/Formats/Png/PngDecoderCore.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ImageSharp/Formats/Png/PngDecoderCore.cs b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
index d9df44a09..633d151b6 100644
--- a/src/ImageSharp/Formats/Png/PngDecoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
@@ -272,7 +272,7 @@ namespace ImageSharp.Formats
         /// <exception cref="System.ArgumentException"><paramref name="bits"/> is less than or equals than zero.</exception>
         private static Span<byte> ToArrayByBitsLength(Span<byte> source, int bytesPerScanline, int bits)
         {
-            Guard.NotNull(source, nameof(source));
+            Guard.MustBeGreaterThan(source.Length, 0, nameof(source));
             Guard.MustBeGreaterThan(bits, 0, nameof(bits));
 
             if (bits >= 8)