Setters should check the input value - i.e. make revert if it is the zero address or zero.
Note: while it has been indicated by the sponsor input validation will be on the front-end side to relieve users from unnecessary gas spendings, this issue here concerns constructor functions or setters called by authorized admins, not users, and most likely by interacting with the contract directly (for instance using Etherscan or Hardhat) and not with a front-end.
5 instances:
function setAdmin(address a)
function setSwivel(address s)
function setAdmin(address a)
function setAdmin(address a)
function setMarketPlace(address m)
Add non-zero checks to the setters aforementioned.
