PHP error when attempting to open a message with a message/rfc822 part

[GTMSMitch]

This error occurs when attempting to view a message which has another message attached as a 'message/rfc822' part. RoundCube displays an "Oops.. Something went wrong!" internal error, and the error logs display "Uncaught TypeError: strtolower(): Argument #1 ($string) must be of type string" on line 2149 in rcube_imap.php. These messages display as expected in other email clients.

I am using Roundcube version 1.6.1, Apache version 2.4.56 and PHP version 8.2.4 but I have tried with previous versions of PHP and Apache and encountered the same issue.

I've attached an example email that causes the issue:
DisplayErrorEmailText.txt

[GTMSMitch]

Update: Can replicate simply by creating an email using RoundCube and either forwarding as an attachment or attaching an EML file using the "Attach a file" button on the right hand side.

I have previously seen attaching EMLs in this way working and displaying as normal because they were attached as a text/html part rather than a message/rfc822 part, however I'm unsure as to what combination of RC / Apache / PHP this was.

[alecpl]

Duplicate of #8803.

[alecpl]

But it supposed to be fixed in 1.6.1 and I'm unable to reproduce using git-master. So, I'm not sure.

[alecpl]

Actually this might be another issue. I was still not able to reproduce and I think it may depend on the content of your IMAP server response. Anyway, I added some code that should prevent the error to appear.