Bug description
During use of Webklex PHP Imap I encountered a problem with non-incoming attachments.
After debugging I found a problem with attachment ID in Message.php file on line 592:
https://github.com/Webklex/php-imap/blob/master/src/Message.php#L592
In my case getId method 4 out of 7 attachments, returns an empty value (an empty string value).

Bug result
Not all attachments are saved by missing attachments in the message.

Proposed solution
One of solution can be changing this line to:

... if (!empty($oAttachment->getId())) { .... 

Is there a chance to improve this part of code?