In ERC777, calling a
tokensReceived) hook is mandatory when sending(or receiving) a token? I wonder if the holder does not register
ERC777TokensSender contract to ERC1820 registry then it is not necessary to call
The Token contract MUST call
tokensToSendhook of the holder if the holder registers an
ERC777TokensSenderimplementation via ERC1820.
I misunderstand something here?