Custom icon using file extension (not mimetype)

Nextcloud version (eg, 12.0.2): 13
Operating system and version (eg, Ubuntu 17.04): Ubuntu 16
Apache or nginx version (eg, Apache 2.4.25): Nginx
PHP version (eg, 7.1): 7.0

The issue you are facing:
I want to display a custom icon for file ending by .ma (Maya 3d software). I am not aware of any mimetype… What can I do?

The file on the server is of type:
file --mime-type -b

Here’s what I tried:

	"ma": ["application/ma", "text/plain"]


        "application/ma": "image"

sudo -u www-data php occ maintenance:mimetype:update-js

But the icon is still of type file.

Should I use a javascript trick to do the job or maybe there’s something I don’t do right (with mimetypemapping)?

Anyone can help me? Just needs an idea on how to fix this. Should I use GIT issue?

Or maybe javascript?