This is gonna be a bit of a weird one b/c I can't provide the actual input for the test case. On the codingGame website there is an exercise where I have to find the lowest difference between integers. I create a variable, but leave it undefined and later use it to hold the lowest difference

function shortest(horses){
  let short;
  horses.sort((a,b) => a - b).forEach((horse,i) => {
    let dif = horse - horses[i-1];
    if (dif < short || !short) short = dif; 
  });
  return short;
};

This passes all the tests but one, and the only way to solve the failed one is to assign a value to short instead of leaving it undefined (like let short = 10000000000000); The website, annoyingly, won't give out the input so I'm not sure why the code is behaving this way so does does anyone know why leaving it undefined instead of a value will cause problems?