Fix occasional NullReferenceException when trying to resolve endpoints

Author: kjnilsson

ChangeLog.md

@@ -5,3 +5,7 @@
 `ConnectionFactory#CreateConnection` could deadlock in some circumstances.
 
 GH issue: [rabbitmq-dotnet-client#239](https://github.com/rabbitmq/rabbitmq-dotnet-client/issues/239).
+
+Occasional NullReferenceException when unable to resolve any endpoints/
+
+GH issue: [rabbitmq-dotnet-client#238](https://github.com/rabbitmq/rabbitmq-dotnet-client/issues/238)

projects/client/RabbitMQ.Client/src/client/api/IEndpointResolverExtensions.cs

@@ -65,7 +65,8 @@ public static T SelectOne<T>(this IEndpointResolver resolver, Func<AmqpTcpEndpoi
                     exception = e;
                 }
             }
-            if(t.Equals(default(T)))
+
+            if(Object.Equals(t, default(T)) && exception != null)
             {
                 throw exception;
             }

projects/client/Unit/src/unit/TestIEndpointResolverExtensions.cs

@@ -0,0 +1,92 @@
+// This source code is dual-licensed under the Apache License, version
+// 2.0, and the Mozilla Public License, version 1.1.
+//
+// The APL v2.0:
+//
+//---------------------------------------------------------------------------
+//   Copyright (c) 2007-2016 Pivotal Software, Inc.
+//
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+//   Unless required by applicable law or agreed to in writing, software
+//   distributed under the License is distributed on an "AS IS" BASIS,
+//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//   See the License for the specific language governing permissions and
+//   limitations under the License.
+//---------------------------------------------------------------------------
+//
+// The MPL v1.1:
+//
+//---------------------------------------------------------------------------
+//  The contents of this file are subject to the Mozilla Public License
+//  Version 1.1 (the "License"); you may not use this file except in
+//  compliance with the License. You may obtain a copy of the License
+//  at http://www.mozilla.org/MPL/
+//
+//  Software distributed under the License is distributed on an "AS IS"
+//  basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+//  the License for the specific language governing rights and
+//  limitations under the License.
+//
+//  The Original Code is RabbitMQ.
+//
+//  The Initial Developer of the Original Code is Pivotal Software, Inc.
+//  Copyright (c) 2007-2016 Pivotal Software, Inc.  All rights reserved.
+//---------------------------------------------------------------------------
+
+using NUnit.Framework;
+using System;
+using System.Collections.Generic;
+using System.Threading;
+
+namespace RabbitMQ.Client.Unit
+{
+    public class TestEndpointResolver : IEndpointResolver
+    {
+        private IEnumerable<AmqpTcpEndpoint> endpoints;
+        public TestEndpointResolver (IEnumerable<AmqpTcpEndpoint> endpoints)
+        {
+            this.endpoints = endpoints;
+        }
+
+        public IEnumerable<AmqpTcpEndpoint> All()
+        {
+            return endpoints;
+        }
+    }
+
+    class TestEndpointException : Exception
+    {
+        public TestEndpointException(string message) : base(message)
+        {
+        }
+    }
+
+    public class TestIEndpointResolverExtensions
+    {
+        [Test]
+        public void SelectOneShouldReturnDefaultWhenThereAreNoEndpoints()
+        {
+            var ep = new TestEndpointResolver(new List<AmqpTcpEndpoint>());
+            Assert.IsNull(ep.SelectOne<AmqpTcpEndpoint>((x) => null));
+        }
+
+        [Test]
+        public void SelectOneShouldRaiseThrownExceptionWhenThereAreOnlyInaccessibleEndpoints()
+        {
+            var ep = new TestEndpointResolver(new List<AmqpTcpEndpoint> { new AmqpTcpEndpoint()});
+            Assert.Throws<TestEndpointException>(() => ep.SelectOne<AmqpTcpEndpoint>((x) => { throw new TestEndpointException("bananas"); }));
+        }
+
+        [Test]
+        public void SelectOneShouldReturnFoundEndpoint()
+        {
+            var ep = new TestEndpointResolver(new List<AmqpTcpEndpoint> { new AmqpTcpEndpoint()});
+            Assert.IsNotNull(ep.SelectOne<AmqpTcpEndpoint>((e) => e));
+        }
+    }
+}