Cannot create a group chat in v10.1.7

[joudinet]

Describe the bug
When I click on the + button to join/create a MUC room and I fill the input text for the name of the room (for example "foo"), the join button does not work. I use a non-federated private XMPP server (ejabberd).

To Reproduce
Steps to reproduce the behavior:

1. Click on '+' button
2. Enter a room name
3. The "Join" remains disabled
4. See error

Expected behavior
I should be able to click on the Join button and create and join the room (on the default conference MUC service).

Environment (please complete the following information):

• Desktop
• Browser: Firefox
• Converse.js version: 10.1.7 (view_mode: "embedded")

Additional context
I tried on the master branch and even though the CSS for the embedded view has several issues, after tweeking it to be able to open the "Enter a new Groupchat" dialog, there it works. The Join button is not disabled and I can create and join the room "foo".
I'm not sure if you were aware that this feature was not working in the current last release of converse.js and I haven't find yet which commit fixed it in the master branch.

[joudinet]

Using the debugger to try to understand the difference between v10.1.7 and master, I think the issue may be related to lit.html, something close to lit/lit#183 even though here, the question mark is used.
In converse v10.1.7, I see the following input in the DOM:
<input type="submit" class="btn btn-primary" name="join" value="Join" disabled="">, thus the input is disabled even though muc_roomid_policy_error_msg is null.
The lit version has been updated from 2.4.0 to 3.1.4, since converse v10.1.7. I'm going to look clues in their release notes.

[jcbrand]

Have you tried using the latest master branch of Converse to see whether the issue is present there as well?

[joudinet]

I've tried it, and the issue is not present using the latest master branch of Converse. That's why I believe the issue is in the lit version, which is not the same version used in Converse v10.1.7.
I do need to use a released version of Converse in my project. So I implemented a workaround in v10.1.7 by removing the disabled property completely, leaving the join button enabled all the time, even in cases where it should be disabled if I understand the code correctly.
I guess we could close this issue because it is fixed in master and I opened it just to let you know it doesn't work on the last released version. Maybe, add a note in the release notes for the next release?