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Sorry to hear you’re facing problems 
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In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 12.0.2):
Operating system and version (eg, Ubuntu 17.04):
Apache or nginx version (eg, Apache 2.4.25): no idea
PHP version (eg, 7.1): 7.2
The issue you are facing:
favicon wont load
it spams logs with errors
Is this the first time you’ve seen this error? (Y/N): n
Steps to replicate it:
- open any page and the favicon wont load. it spams errors in logs
The output of your Nextcloud log in Admin > Logging:
[index] Error: Error: Call to undefined function OCA\Theming\mime_content_type() at <<closure>>
0. /home/scaryamm/cloud.scaring.xyz/apps/theming/lib/IconBuilder.php line 69
renderAppIcon("settings", 128)
1. /home/scaryamm/cloud.scaring.xyz/apps/theming/lib/Controller/IconController.php line 126
getFavicon("settings")
2. /home/scaryamm/cloud.scaring.xyz/lib/private/AppFramework/Http/Dispatcher.php line 166
getFavicon("settings")
3. /home/scaryamm/cloud.scaring.xyz/lib/private/AppFramework/Http/Dispatcher.php line 99
executeController(OCA\Theming\Controller\IconController {}, "getFavicon")
4. /home/scaryamm/cloud.scaring.xyz/lib/private/AppFramework/App.php line 118
dispatch(OCA\Theming\Controller\IconController {}, "getFavicon")
5. /home/scaryamm/cloud.scaring.xyz/lib/private/AppFramework/Routing/RouteActionHandler.php line 47
main("OCA\\Theming\\C ... r", "getFavicon", OC\AppFramework\ ... {}, {app: "settings" ... "})
6. <<closure>>
__invoke({app: "settings" ... "})
7. /home/scaryamm/cloud.scaring.xyz/lib/private/Route/Router.php line 297
call_user_func(OC\AppFramework\ ... {}, {app: "settings" ... "})
8. /home/scaryamm/cloud.scaring.xyz/lib/base.php line 987
match("/apps/theming/favicon/settings")
9. /home/scaryamm/cloud.scaring.xyz/index.php line 42
handleRequest()
GET /index.php/apps/theming/favicon/settings?v=4
from (my ip) by Scaring at 2019-02-27T18:29:25+00:00
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
no idea how to find
The output of your Apache/nginx/system log in /var/log/____:
no idea how to find