Fix a bug where adding superadmins would crash if none existed before

[Nomafin]

The add command crashes if there are no super admins present when trying to add a new one thus prevents the admin fixing the situation.

Returning empty array instead of null from the get_admins() function prevents the crash because in_array() on line 107 expects an array.

[schlessera]

Just casting to (array) here should do the exact same thing.

[schlessera]

Thanks for the pull request, @Nomafin !

I think the above problem can be solved with a simple cast to (array). This would turn a null result into an empty array instead.

[Nomafin]

Yeah, this is definitely simpler approach. I actually thought this as well, but decided for the if clause for better readability. But I agree that this would do as well.

[schlessera]

Yes, I can see why the if clause might be more readable.

However, I think that the if clause also implies there is some logic being done here. This is not the case, though, we just fix the type of the return value of the WordPress function, as the WordPress return value is just borked in this case.

[schlessera]

@Nomafin Would you be up to adding a test for this error case as well, to make sure the WP behavior never changes and we don't introduce a regression later on?

[schlessera]

@Nomafin I will work on the tests for this myself in the coming days to close this PR.

[javorszky]

I think I ran into this exact problem, with some more verbose errors:

Warning: count(): Parameter must be an array or an object that implements Countable in phar:///usr/local/bin/wp/vendor/wp-cli/super-admin-command/src/Super_Admin_Command.php on line 104
Warning: in_array() expects parameter 2 to be array, string given in phar:///usr/local/bin/wp/vendor/wp-cli/super-admin-command/src/Super_Admin_Command.php on line 107
Fatal error: Uncaught Error: [] operator not supported for strings in phar:///usr/local/bin/wp/vendor/wp-cli/super-admin-command/src/Super_Admin_Command.php:112
Stack trace:
#0 [internal function]: Super_Admin_Command->add(Array, Array)
#1 phar:///usr/local/bin/wp/php/WP_CLI/Dispatcher/CommandFactory.php(89): call_user_func(Array, Array, Array)
#2 [internal function]: WP_CLI\Dispatcher\CommandFactory::WP_CLI\Dispatcher\{closure}(Array, Array)
#3 phar:///usr/local/bin/wp/php/WP_CLI/Dispatcher/Subcommand.php(425): call_user_func(Object(Closure), Array, Array)
#4 phar:///usr/local/bin/wp/php/WP_CLI/Runner.php(353): WP_CLI\Dispatcher\Subcommand->invoke(Array, Array, Array)
#5 phar:///usr/local/bin/wp/php/WP_CLI/Runner.php(376): WP_CLI\Runner->run_command(Array, Array)
#6 phar:///usr/local/bin/wp/php/WP_CLI/Runner.php(1102): WP_CLI\Runner->_run_command_and_exit()
#7 phar:///usr/local/bin/wp/php/WP_CLI/Bootstrap/LaunchRunner.php(23): WP_CLI\Runner->start()
#8 phar:///usr/local/bin/wp/php/bootstrap.php(75): WP_CLI\Bootstrap\Laun in phar:///usr/local/bin/wp/vendor/wp-cli/super-admin-command/src/Super_Admin_Command.php on line 112