From 774d49a908a62b893f67f9b6a07894bfd01cd386 Mon Sep 17 00:00:00 2001
From: PMExtra <pm@jubeat.net>
Date: Fri, 3 Apr 2020 14:49:39 +0800
Subject: [PATCH] Fix exception message and add test cases.

---
 Source/MQTTnet/Extensions/UserPropertyExtension.cs       | 2 +-
 Tests/MQTTnet.Core.Tests/MqttApplicationMessage_Tests.cs | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Source/MQTTnet/Extensions/UserPropertyExtension.cs b/Source/MQTTnet/Extensions/UserPropertyExtension.cs
index e950141..5bb28cf 100644
--- a/Source/MQTTnet/Extensions/UserPropertyExtension.cs
+++ b/Source/MQTTnet/Extensions/UserPropertyExtension.cs
@@ -25,7 +25,7 @@ namespace MQTTnet.Extensions
             }
             catch (Exception ex)
             {
-                throw new InvalidOperationException($"Cannot convert value({value}) of UserProperty({propertyName}) to {typeof(T).FullName}.", ex);
+                throw new InvalidOperationException($"Cannot convert value({value ?? "null"}) of UserProperty({propertyName}) to {typeof(T).FullName}.", ex);
             }
         }
     }
diff --git a/Tests/MQTTnet.Core.Tests/MqttApplicationMessage_Tests.cs b/Tests/MQTTnet.Core.Tests/MqttApplicationMessage_Tests.cs
index 073e4c4..6b791dc 100644
--- a/Tests/MQTTnet.Core.Tests/MqttApplicationMessage_Tests.cs
+++ b/Tests/MQTTnet.Core.Tests/MqttApplicationMessage_Tests.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Extensions;
@@ -24,6 +25,9 @@ namespace MQTTnet.Tests
             Assert.AreEqual("bar", message.GetUserProperty("foo"));
             Assert.AreEqual(1011, message.GetUserProperty<int>("value"));
             Assert.AreEqual("insensitive", message.GetUserProperty("case"));
+            Assert.AreEqual(null, message.GetUserProperty("nonExists"));
+            Assert.AreEqual(null, message.GetUserProperty<int?>("nonExists"));
+            Assert.ThrowsException<InvalidOperationException>(() => message.GetUserProperty<int>("nonExists"));
         }
     }
 }