Error with php 7.3 and EE 6.x

[nutella]

Error Caught Call to a member function getFrontendClass() on null ee/legacy/libraries/Template.php:1641

Stack Trace: Please include when reporting this error

0 ee/legacy/libraries/Template.php(1386): EE_Template->process_tags()

1 ee/legacy/libraries/Template.php(560): EE_Template->tags()

2 ee/legacy/libraries/Template.php(228): EE_Template->parse('{!-- ra:0000000...', true, 1, false)

3 ee/legacy/libraries/Template.php(1070): EE_Template->fetch_and_parse('common', 'page_footer', true, 1)

4 ee/legacy/libraries/Template.php(602): EE_Template->process_sub_templates('{!-- ra:0000000...')

5 ee/legacy/libraries/Template.php(228): EE_Template->parse('{!-- ra:0000000...', false, 1, false)

6 ee/legacy/libraries/Template.php(163): EE_Template->fetch_and_parse('', Array, false)

7 ee/legacy/libraries/Core.php(647): EE_Template->run_template_engine('', '')

8 ee/legacy/controllers/ee.php(53): EE_Core->generate_page()

9 [internal function]: EE->index()

10 ee/ExpressionEngine/Core/Core.php(251): call_user_func_array(Array, Array)

11 ee/ExpressionEngine/Core/Core.php(111): ExpressionEngine\Core\Core->runController(Array)

12 ee/ExpressionEngine/Boot/boot.php(161): ExpressionEngine\Core\Core->run(Object(ExpressionEngine\Core\Request))

13 index.php(164): require_once('...')

13 index.php(164): require_once('...')

Only if I enable gwcode_categories.