public function parseOptional(OptionalNode $optionalNode)
 {
     $bool = $this->parser->readBit();
     if ($bool !== 0) {
         return $this->parse($optionalNode->getIndex());
     }
     return NULL;
 }
 public function parseOptional(OptionalNode $optionalNode)
 {
     $this->expectSkip(4);
     $bool = $this->parser->readBits(8);
     if ($bool != 0) {
         return $this->parse($optionalNode->getIndex());
     }
     return NULL;
 }