code: public function getPdo($connection = null)
  	{
  		if ($connection === null) {
  			$connection = $this->defaultConnection;
  		}
  
  		if (isset($this->instances[$connection])) {
  			return $this->instances[$connection];
  		}
  
  		$config = $this->getConnectionConfig($connection);
  
  		return $this->instances[$connection] = $this->factory->makePdo($config, $connection);
  	}
docs: Get a PDO instance.
  
  @param  string|null $connection Null fetches the default connection.
  
  @return \PDO