Caesars Cipher, From ASCII to Letters

Tell us what’s happening:

Hi guys I dont know why when I am trying to translate from ascii to letters I am getting this error “porTraducir.fromCharCode is not a function”…
Your code so far

function rot13(str) { // LBH QVQ VG!
 var newArray = [];
  var porTraducir=[];
  var letters=[];
  var corto= str.split("");

   for (var i=0; i<corto.length; i++){ 
   var nueva= str.charCodeAt(i); 
   newArray.push(nueva);               // Convert to ascii
  for (var b=0; b<newArray.length; b++){ 
   var newNums=[];
    if (newArray[b] < 78 && newArray[b] >= 65 ) {
      newNums = newArray[b] + 13;
    } else if (newArray[b] >= 78) {
      newNums = newArray[b] - 13;
    } else if (newArray[b] == 32) {
      newNums = newArray[b];
 for (var c = 0; c < porTraducir.length; c++){ 
   var nueva2= porTraducir.fromCharCode(c);  // Convert to letters

return letters; 

// Change the inputs below to test
rot13("SERR PBQR PNZC");```
**Your browser information:**

Your Browser User Agent is: ```Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.36```.

**Link to the challenge:**

Your var porTraducir=[]; is an array and fromCharCode needs a string.

I found the solution doing this:

 var charCodeToString = String.fromCharCode.apply(null, porTraducir);  

  return charCodeToString; 

But I am not sure about what Null does.

null Mira aquí compa.

Gracias Mario! pero por que al usar null antes de porTraducir soluciona el error?