Hey there, having some trouble with my code. It seems to be returning an empty array and I’m not sure why…help please!

function validateCred(arr) {

const doubles = ;

let sum = 0;

for (let i = 15; i >= 0; i–) {

let start = arr[i];

if (i % 2 === 0) {

start *= 2

if (start > 9) {

start -= 9;

}

}

doubles.unshift(start);

}

return doubles;

sum += start;

if (sum % 10 === 0) {

return true;

}

}

function findInvalidCards(arr) {

let check = ;

for (let j = 0; j < arr.length; j++) {

if ((validateCred(arr[j])) === false) {

check.push(arr[j]);

}

}

return check;

}