Make ApiError is never null

Octokit.Tests/Exceptions/ApiValidationExceptionTests.cs

@@ -1,4 +1,5 @@
-using System.IO;
+using System;
+using System.IO;
 using System.Linq;
 using System.Runtime.Serialization.Formatters.Binary;
 using NSubstitute;
@@ -39,6 +40,22 @@ namespace Octokit.Tests.Exceptions
                 Assert.Equal(responseContent, exception.ApiValidationError.Message);
             }
 
+            [Fact]
+            public void CreatesEmptyGitHubErrorWhenResponseBodyIsNull()
+            {
+                var response = Substitute.For<IResponse>();
+                response.Body.Returns("test");
+
+                var exception = new ApiValidationException();
+                var anotherException = new ApiValidationException("message1");
+                var thirdException = new ApiValidationException("message2", new InvalidOperationException());
+
+                // It's fine if the message is null when there's no response body as long as this doesn't throw.
+                Assert.Null(exception.ApiValidationError.Message);
+                Assert.Equal("message1", anotherException.ApiValidationError.Message);
+                Assert.Equal("message2", thirdException.ApiValidationError.Message);
+            }
+
 #if !NETFX_CORE
             [Fact]
             public void CanPopulateObjectFromSerializedData()

Octokit/Exceptions/ApiValidationException.cs

@@ -17,16 +17,17 @@ namespace Octokit
         static readonly IJsonSerializer _jsonSerializer = new SimpleJsonSerializer();
 
         public ApiValidationException()
+            : this(new ApiError(), null)
         {
         }
 
         public ApiValidationException(string message)
-            : base(message)
+            : this(new ApiError { Message = message }, null)
         {
         }
 
         public ApiValidationException(string message, Exception innerException)
-            : base(message, innerException)
+            : this(new ApiError { Message = message }, innerException)
         {
         }
 
@@ -75,7 +76,10 @@ namespace Octokit
             try
             {
                 if (responseContent != null)
-                    return _jsonSerializer.Deserialize<ApiError>(responseContent) ?? new ApiError { Message = responseContent };
+                {
+                    return _jsonSerializer.Deserialize<ApiError>(responseContent)
+                        ?? new ApiError { Message = responseContent };
+                }
             }
             catch (Exception)
             {