I have recently upgraded my Rails application from version 5.2 to 6.1. After the upgrade, everything appears to be functioning correctly, except my controller test cases are now throwing the following error:

undefined method `merge’ for nil:NilClass

Here is the complete stack trace of the error:

Interestingly, the test cases for other classes and services work as expected. Has anyone else encountered this issue, or does anyone have any insights into what might be causing this error?

Any help or guidance would be greatly appreciated!