I bumped into this interesting bug when one of my database tables became corrupt.

Steps to reproduce the issue

Install Joomla 4 on a PHP 8.0 host. The PHP version is important.

(optional) Set Site Debug to Yes and Error Reporting to Maximum.

Pick a view which uses Empty State, e.g. articles.

Sabotage your database to cause a SQL error — this emulates the effects of having a corrupt table or a Joomla update failing to apply schema changes. For articles, sabotage the #__content table, e.g. rename a column which is used in the view.

Expected result

You get a Joomla error page about a SQL error which helps you identify and fix the root cause.

Actual result

You get a PHP error (InvalidArgumentException).

If you turned on Site Debug you will see that it points out to this code:

if (!\count($this->items) && $this->isEmptyState = $this->get('IsEmptyState'))
{
	$this->setLayout('emptystate');
}

It complains that $this->items is a boolean, not countable.

System information (as much as possible)

PHP 8.0 is the only relevant piece of system information.

Additional comments

When a SQL error occurs, ListModel::getItems returns boolean false. In PHP 7 trying to count() a non–countable scalar would result in a warning. On PHP 8 this is an InvalidArgumentException which causes a stop error.

There are two ways to deal with it.

The architecturally correct solution is to change the first line of that if–block to read

if (\is_countable($this->items) && !\count($this->items) && $this->isEmptyState = $this->get('IsEmptyState'))
{
	$this->setLayout('emptystate');
}

However, it's not viable for Joomla 4 since is_countable is only available on PHP 7.3 and later when the Countable interface was added to the language. Joomla requires PHP 7.2 or later. If we insist on supporting PHP 7.2 this won't work.

This brings us to the second solution. All HtmlView classes which implement Empty State also have this piece of code to check for errors:

// Check for errors.
if (\count($errors = $this->get('Errors')) || $this->transitions === false)
{
	throw new GenericDataException(implode("\n", $errors), 500);
}

Moving that if–block above the Empty State if–block resolves the problem.

Pinging @PhilETaylor since he added the Empty State code to Joomla.