Use object.ReferenceEquals for reference type equality comparison (#1277)

Author: paulomorgado

src/core/SIP/SIPEndPoint.cs

@@ -244,7 +244,7 @@ public override bool Equals(object obj)
 
         public static bool operator ==(SIPEndPoint endPoint1, SIPEndPoint endPoint2)
         {
-            if ((object)endPoint1 == null && (object)endPoint2 == null)
+            if (object.ReferenceEquals(endPoint1, endPoint2))
             {
                 return true;
             }

src/core/SIP/SIPParameters.cs

@@ -1,4 +1,4 @@
-//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
 // Filename: SIPParameters.cs
 //
 // Description: SIP parameters as used in Contact, To, From and Via SIP headers.
@@ -16,6 +16,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net;
 using System.Runtime.Serialization;
 using Microsoft.Extensions.Logging;
 using SIPSorcery.Sys;
@@ -337,7 +338,7 @@ public override bool Equals(object obj)
         /// </summary>
         public static bool operator ==(SIPParameters x, SIPParameters y)
         {
-            if (x is null && y is null)
+            if (object.ReferenceEquals(x, y))
             {
                 return true;
             }

src/core/SIP/SIPURI.cs

@@ -1,4 +1,4 @@
-//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
 // Filename: SIPURI.cs
 //
 // Description: SIP URI.
@@ -605,7 +605,7 @@ public override bool Equals(object obj)
 
         public static bool operator ==(SIPURI uri1, SIPURI uri2)
         {
-            if (uri1 is null && uri2 is null)
+            if (object.ReferenceEquals(uri1, uri2))
             {
                 return true;
             }

src/net/STUN/STUNUri.cs

@@ -268,7 +268,7 @@ public override bool Equals(object obj)
 
         public static bool operator ==(STUNUri uri1, STUNUri uri2)
         {
-            if (uri1 is null && uri2 is null)
+            if (object.ReferenceEquals(uri1, uri2))
             {
                 return true;
             }