Argument #1 ($ftp) must be of type FTP\Connection, null given

My WordPress crashed, while I was activating Rank Math.

I immediately deactivated the Rank Math plugin by modifying the database, and my WordPress recovered.

After that, I checked the error message and it displayed the following:

And the code is here:

So, the root cause was using $this->link without checking.

I added checking as follows:

It worked, and Rank Math could be activated without crashing.

However, a new issue arose – my Avada crashed:

The error message showed these:

Root cause was the same, using $this->link without checking.

This time, I added checking before using in all functions in this file, it worked, both Rank Math and Avada were normal(Maybe there were new issues I hadn’t come across).

Furthermore, I haven’t enbaled FTP on my server, and my relevant ENV information: