code: protected function processValue($value)/*# : string */
      {
          // object
          if (is_object($value)) {
              if ($value instanceof RawInterface) {
                  return $value->getStatement([], false);
              } elseif ($value instanceof StatementInterface) {
                  return '(' . $value->getStatement([], false) . ')';
              }
          }
  
          // scalar
          if (is_null($value)) {
              return 'NULL';
          } else {
              return $this->getPlaceholder($value);
          }
      }
docs: Process value
  
  @param  mixed $value
  @return string placeholder or value
  @access protected