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Looks like we got a little detail out of sequence.
The Xmf\Request::hasVar() method was added to XMF after XOOPS 2.5.8 was released. The current Publisher version was developed along with XOOPS 2.5.9, which does include that method. I'm not totally sure, but it looks like it was my mistake. Sorry!
There are a couple of ways you could fix it today.
If you are comfortable using composer, running the following command in the class/libraries directory would update XMF to the current version:
composer update
Alternatively, you could update just the Request class file, by copying this file:
https://raw.githubusercontent.com/XOOPS/xmf/v1.2.10/src/Xmf/Request.phpover this file in your XOOPS installation:
class/libraries/vendor/xoops/xmf/src/Xmf/Request.php
Either one of those should get you through the error you are encountering.