Using Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition::cannotBeEmpty() at path "liip_monitor.mailer.recipient" has no effect, consider requiresAtLeastOneElement() instead. In 4.0 both methods will behave the same.
See symfony source code, it's a @trigger_error in sf3 and an exception in sf4 :
Here is the warning when using symfony 3.4 :
See symfony source code, it's a
@trigger_error
in sf3 and an exception in sf4 :A similar fix can be viewed in another bundle : https://github.com/nelmio/NelmioJsLoggerBundle/pull/20