code: private static function initStaticValues()
  	{
  		if (self::$utmCookieName === null) {
  			self::$utmCookieName = 'utm';
  		}
  
  		self::$utmCookie = [
  			'utm_campaign' => null, 
  			'utm_medium'   => null, 
  			'utm_source'   => null, 
  			'utm_term'     => null, 
  			'utm_content'  => null
  		];
  
  		
  		if (self::$lifetime === null) {
  			self::$lifetime = new DateInterval(self::DEFAULT_UTM_COOKIE_LIFETIME);
  		}
  
  		if (self::$overwrite === null) {
  			self::$overwrite = true;
  		}
  	}
docs: Initialize static values to default (or empty) values.