<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def dispatch_hook(cls, s=None, *_args, **_kwds):
 # type: (Optional[str], *Any, **Any) -> base_classes.Packet_metaclass """dispatch_hook returns the subclass of HPackHeaders that must be used to dissect the string. """

        if s is None:
            return config.conf.raw_layer
        fb = orb(s[0])
        if fb & 0x80 != 0:
            return HPackIndexedHdr
        if fb & 0x40 != 0:
            return HPackLitHdrFldWithIncrIndexing
        if fb & 0x20 != 0:
            return HPackDynamicSizeUpdate
        return HPackLitHdrFldWithoutIndexing