From 77caaf8c72bced85116fabdcec537e4aa8e59bb9 Mon Sep 17 00:00:00 2001
From: Bob Thomas <bthomas@tripwire.com>
Date: Fri, 27 Apr 2018 09:01:48 -0400
Subject: [PATCH] Cast a null MediaRange reference to a null string

When trying to compare a null MediaRange to a string, the implicit cast to string was throwing a NullReferenceException. Fix the operator so that a null MediaRange is cast to a null string.
---
 src/Nancy/Responses/Negotiation/MediaRange.cs     |  5 +++++
 .../Responses/Negotiation/MediaRangeFixture.cs    | 15 ++++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/Nancy/Responses/Negotiation/MediaRange.cs b/src/Nancy/Responses/Negotiation/MediaRange.cs
index f8cdf3950a..893585b457 100644
--- a/src/Nancy/Responses/Negotiation/MediaRange.cs
+++ b/src/Nancy/Responses/Negotiation/MediaRange.cs
@@ -122,6 +122,11 @@ public bool MatchesWithParameters(MediaRange other)
         /// </returns>
         public static implicit operator string(MediaRange mediaRange)
         {
+            if (null == mediaRange)
+            {
+                return null;
+            }
+
             if (mediaRange.Parameters.Any())
             {
                 return string.Concat(mediaRange.Type, "/", mediaRange.Subtype, ";", mediaRange.Parameters);
diff --git a/test/Nancy.Tests/Unit/Responses/Negotiation/MediaRangeFixture.cs b/test/Nancy.Tests/Unit/Responses/Negotiation/MediaRangeFixture.cs
index 208ce846f9..23dba98d85 100644
--- a/test/Nancy.Tests/Unit/Responses/Negotiation/MediaRangeFixture.cs
+++ b/test/Nancy.Tests/Unit/Responses/Negotiation/MediaRangeFixture.cs
@@ -83,5 +83,18 @@ public void Should_strip_whitespace_when_calling_tostring()
             // Then
             range.ToString().ShouldEqual("application/vnd.nancy;a=1;b=2");
         }
+
+        [Fact]
+        public void Should_cast_to_null_string()
+        {
+            // Given
+            MediaRange range = null;
+
+            // When
+            string cast = (string)range;
+
+            // Then
+            Assert.Null(cast);
+        }
     }
-}
\ No newline at end of file
+}