ModelExtensions fix

src/Correo.MailKit/Extensions/ModelExtensions.cs

@@ -11,6 +11,9 @@ namespace Correo.MailKit.Extensions
 
         private static void AddRange(this InternetAddressList list, IEnumerable<EmailMessage.MailAddress> addresses)
         {
+            if (addresses == null)
+                return;
+
             foreach (var item in addresses)
                 list.Add(item.ToMailboxAddress());
         }

src/Correo.SmtpClient/Extensions/ModelExtensions.cs

@@ -11,6 +11,9 @@ namespace Correo.SmtpClient.Extensions
 
         private static void AddRange(this MailAddressCollection collection, IEnumerable<EmailMessage.MailAddress> addresses)
         {
+            if (addresses == null)
+                return;
+
             foreach (var item in addresses)
                 collection.Add(item.ToMailAddress());
         }