code: public function format($event)
  	{
  		$output = $this->format;
  
  		if (array_key_exists('extra', $event) === true)
  		{
  			$this->formatExtra($event, $event['extra']);
  			$event['message'] = 'Missing Key:';
  		}
  		else
  		{
  			$event['extra'] = [];
  		}
  
  		foreach ($event as $name => $value)
  		{
  			if (is_array($value) === true && count($value) === 0)
  			{
  				$value = '';
  			}
  			else
  			{
  				$value = $this->normalize($value);
  			}
  
  			$output = str_replace('%' . $name . '%', $value, $output);
  		}
  
  		return trim($output);
  	}
docs: Formats data into a single line to be written by the writer.
  
  @param array $event event data
  @return string formatted line to write to the log