Adding a return function to Truffles Pet Shop - solidity

Question

I am following the Truffle tutorials, and am on https://www.trufflesuite.com/tutorials/pet-shop. I would like to add a return function that sets the adopters[PetId] in the solidity contract back to the 0 address. I currently have:
function returnPet(uint petId) public returns (uint) {
require(petId >= 0 && petId <= 15);
adopters[petId] = msg.sender;
return petId;
}
in my Adoption.sol
and in my app.js is:
handleReturn: function(event) {
event.preventDefault();
var petId = parseInt($(event.target).data('id'));
var adoptionInstance;
web3.eth.getAccounts(function(error, accounts) {
if (error) {
console.log(error);
}
var account = accounts[0];
App.contracts.Adoption.deployed().then(function(instance) {
adoptionInstance = instance;
return adoptionInstance.returnPet(petId);
}).then(function(result) {
return App.markAdopted();
}).catch(function(err) {
console.log(err.message);
});
});
but it hits the catch and returns: invalid address.
In short:
How do I zero out an address in an array of addresses?emphasized text

Answer 1

Your current code in returnPet() sets the adopters[petId] value to msg.sender, which means "the caller address".
I would like to add a return function that sets the adopters[PetId] in the solidity contract back to the 0 address
You can do it by setting the value to address(0).
So your function will then look like
function returnPet(uint petId) public returns (uint) {
require(petId >= 0 && petId <= 15);
adopters[petId] = address(0);
return petId;
}