Dependencies: Update MailKit to 4.15.1

Directory.Packages.props

@@ -50,13 +50,7 @@
     <PackageVersion Include="HtmlAgilityPack" Version="1.12.4" />
     <PackageVersion Include="JsonPatch.Net" Version="3.3.0" />
     <PackageVersion Include="K4os.Compression.LZ4" Version="1.3.8" />
-
-    <!-- TODO (V18): Upgrade MailKit to 4.15.0+.
-         The 4.15.0 update tightened nullability annotations on InternetAddress.TryParse, causing CS8600/CS8601 errors in EmailMessageExtensions.cs.
-         We could fix those of course, but this could cause breaking changes for implentation projects too.
-         So this dependency shouldn't be upgraded beyond 4.14.* until we can do a major version bump for Umbraco 18.
-         -->
-    <PackageVersion Include="MailKit" Version="4.14.1" />
+    <PackageVersion Include="MailKit" Version="4.15.1" />
     <PackageVersion Include="Markdig" Version="0.45.0" />
     <PackageVersion Include="Markdown" Version="2.2.1" />
     <PackageVersion Include="MessagePack" Version="3.1.4" />

src/Umbraco.Infrastructure/Extensions/EmailMessageExtensions.cs

@@ -10,42 +10,42 @@
     {
         var fromEmail = string.IsNullOrEmpty(mailMessage.From) ? configuredFromAddress : mailMessage.From;
 
-        if (!InternetAddress.TryParse(fromEmail, out InternetAddress fromAddress))
+        if (InternetAddress.TryParse(fromEmail, out InternetAddress? fromAddress) is false)
         {
             throw new ArgumentException(
                 $"Email could not be sent.  Could not parse from address {fromEmail} as a valid email address.");
         }
 
-        var messageToSend = new MimeMessage { From = { fromAddress }, Subject = mailMessage.Subject };
+        var messageToSend = new MimeMessage { From = { fromAddress }, Subject = mailMessage.Subject ?? string.Empty };
 
         AddAddresses(messageToSend, mailMessage.To, x => x.To, true);
         AddAddresses(messageToSend, mailMessage.Cc, x => x.Cc);
         AddAddresses(messageToSend, mailMessage.Bcc, x => x.Bcc);
         AddAddresses(messageToSend, mailMessage.ReplyTo, x => x.ReplyTo);
 
         if (mailMessage.HasAttachments)
         {
             var builder = new BodyBuilder();
             if (mailMessage.IsBodyHtml)
             {
                 builder.HtmlBody = mailMessage.Body;
             }
             else
             {
                 builder.TextBody = mailMessage.Body;
             }
 
             foreach (EmailMessageAttachment attachment in mailMessage.Attachments!)
             {
                 builder.Attachments.Add(attachment.FileName, attachment.Stream);
             }
 
             messageToSend.Body = builder.ToMessageBody();
         }
         else
         {
             messageToSend.Body =
-                new TextPart(mailMessage.IsBodyHtml ? TextFormat.Html : TextFormat.Plain) { Text = mailMessage.Body };
+                new TextPart(mailMessage.IsBodyHtml ? TextFormat.Html : TextFormat.Plain) { Text = mailMessage.Body ?? string.Empty };
         }
 
         return messageToSend;
@@ -78,7 +78,7 @@
         {
             foreach (var address in addresses)
             {
-                if (InternetAddress.TryParse(address, out InternetAddress internetAddress))
+                if (InternetAddress.TryParse(address, out InternetAddress? internetAddress))
                 {
                     addressListGetter(message).Add(internetAddress);
                     foundValid = true;
@@ -94,12 +94,10 @@
 
     private static NotificationEmailAddress? ToNotificationAddress(string? address)
     {
-        if (InternetAddress.TryParse(address, out InternetAddress internetAddress))
+        if (InternetAddress.TryParse(address, out InternetAddress? internetAddress) &&
+            internetAddress is MailboxAddress mailboxAddress)
         {
-            if (internetAddress is MailboxAddress mailboxAddress)
-            {
-                return new NotificationEmailAddress(mailboxAddress.Address, internetAddress.Name);
-            }
+            return new NotificationEmailAddress(mailboxAddress.Address, internetAddress.Name ?? string.Empty);
         }
 
         return null;