WARNING: Structure does not match expected primitive cell

On Ubuntu 20.04.3 LTS, I try to install and test ifermi as follows:

$ pyenv shell datasci
$ git clone https://github.com/fermisurfaces/IFermi.git IFermi.git 
$ cd IFermi.git 
$ pip install -r requirements.txt
$ pip install -e .
$ cd examples/MgB2
$ ifermi plot --output fermi-surface.jpg
WARNING: Structure does not match expected primitive cell

Saving plot to fermi-surface.jpg

As you can see, there is a warning triggered. Any hints for fixing it?

Regards,
HZ