Steps to reproduce the issue

1. Install Weblinks 3.6.0 Package from https://extensions.joomla.org/extensions/extension/official-extensions/weblinks/ on Joomla 3.9.0 using PHP 7.2 and set to report PHP warnings.
2. Go to Components - Web Links and add any URL as New Web Link to the existing category Uncategorised with default options, Save & Close.
3. Create a new menu item and select Web Links - List All Web Link Categories with default options, Save & Close.
4. Go to the front end and select the new link.

Expected result

The list shows the category Uncategorised.

Actual result

Warning: count(): Parameter must be an array or an object that implements Countable in C:\www\joomla380\components\com_weblinks\models\categories.php on line 95

The list shows the category Uncategorised.

System information (as much as possible)

Joomla 3.9.0
PHP 7.2.11

Additional comments

Fixed by inserting the following lines before line 95 in
components/com_weblinks/models/categories.php

	if (!is_array($this->_items))
	{
		$this->_items	= array();
	}

Ref. topic "Weblinks Categories page - Warning: count() at https://forum.joomla.org/viewtopic.php?f=715&t=967481