Empty Sender header

[yurikuzn]

When sending email using Zend SMTP transport it adds Sender header with empty value if this header was not defined:

Sender: 

If you parse such an email using Zend Imap it throws an error:

Zend\Mail\Header\Exception\InvalidArgumentException: Invalid header value for Sender string

[eth8505]

This was fixed with 2.7.3 #93