code: public function getMaster()
      {
          if ($this->_master === false) {
              $this->_master = $this->shuffleMasters
                  ? $this->openFromPool($this->masters, $this->masterConfig)
                  : $this->openFromPoolSequentially($this->masters, $this->masterConfig);
          }
  
          return $this->_master;
      }
docs: Returns the currently active master connection.
  If this method is called for the first time, it will try to open a master connection.
  @return Connection the currently active master connection. `null` is returned if there is no master available.
  @since 2.0.11