code: public function getChannel($channel = null)
  	{
  		$channel = $channel ?: $this->defaultChannel;
  
  		if (isset($this->deferredChannels[$channel])) {
  			$this->setChannel($channel, $this->deferredChannels[$channel]());
  			unset($this->deferredChannels[$channel]);
  		}
  
  		if (isset($this->channels[$channel])) {
  			return $this->channels[$channel];
  		}
  
  		throw new InvalidArgumentException("Undefined channel: $channel");
  	}
docs: Get a specific channel.
  
  @param  string $channel  Optional - if none, use default channel
  
  @return \Psr\Log\LoggerInterface
  
  @throws InvalidArgumentException If the channel is not defined.