I investigated the NullReferenceException in lesson 11 practice 1 when the answer “Sort E-mails.xaml” is running.
I think the answer “Sort E-mails.xaml” is not appropriate.
Because according to RFC 2822 “Internet Message Format”
3.6.2. Originator fields
If the originator of the message can be indicated by a single mailbox and the author and transmitter are identical, the “Sender:” field SHOULD NOT be used.
I think the answer “Sort E-mails.xaml” have to update mail.From instead of mail.Sender.
NOTE:RFC 2822 Internet Message Format