src/log4php/LoggerRoot.php
public function setLevel(LoggerLevel $level = null) {
		if (isset($level)) {
			parent::setLevel($level);
		} else {
			trigger_error("log4php: Cannot set LoggerRoot level to null.", E_USER_WARNING);
		}
	}
public function setLevel(LoggerLevel $level = null) {
		if (isset($level)) {
			parent::setLevel($level);
		} else {
			trigger_error("log4php: Cannot set LoggerRoot level to null.", E_USER_WARNING);
		}
	}
Override level setter to prevent setting the root logger's level to
null. Root logger must always have a level.

@param LoggerLevel $level