Create an article.

In the intro add the text 'hello'.  High light it, click the link icon.  In the 'Link to' enter 'http:// http://example.com'

Publish. 

An exception is thrown

Argument 2 passed to Symfony\Component\Validator\Util\PropertyPath::append() must be of the type string, null given, called in /var/www/vendor/ezsystems/ezplatform-content-forms/src/lib/Validator/Constraints/FieldValueValidator.php on line 92

Expected a validation error.