Error Adding New Document Set (From Custom Content Type) JSOM

Hello,

I couldn't find a forum here for SharePoint 2016 which is why I'm posting in the 2013 forum. I have created a document library in SharePoint 2016 and assigned a custom content type that I created deriving from DocumentSet. I added all the columns I wanted to this custom document set. The fields consist of text, lookup fields that allow multiple values, and there is also a User field.

Below is my code for the add new form where the error is occurring.

function WebForm_DoPostBackCustom(){  
// GET FORM DATA & VALIDATE  
///....HIDING THIS CODE FOR SIMPLICITY              
// CREATE OBJECT TO SEND TO SHAREPOINT LIST  
var properties = {};  
properties['Title'] = name; //TEXT FIELD  
properties['FileLeafRef'] = name; //? NOT SURE IF I NEED THIS  
properties['Item_x0020_Code'] = itemCode; //TEXT FIELD  
properties['Change_x0020_Control_x0020__x0023_'] = changeControl;//NUMBER FIELD  
properties['Countries'] = countries;//TEXT FIELD  
properties['Justification_x0020__x0026__x0020_Impact_x0020_of_x0020_NOT_x0020_Doing_x0020_Change'] = justification; //TEXT FIELD  
properties['Market_x0020_Notification'] = marketNotification;//TEXT FIELD  
properties['Distributor_x0020_Notification'] = distributorNotification;//TEXT FIELD  
properties['Department_x0020_Expert'] = departmentExpert; //THIS IS A PERSON FIELD              
var selectedChangeTypes = [];   
for (var i = 0; i < changeTypes.length; i++)  
{     
   var newLookupField = new SP.FieldLookupValue();     
   newLookupField.set_lookupId(changeTypes[i]);     
   selectedChangeTypes.push(newLookupField);  
}      
properties['Change_x0020_Types'] = selectedChangeTypes;//MULTI VALUE LOOKUP FIELD              

var selectedImpacts = [];  
for (var i = 0; i < impacts.length; i++)  
{    
  var newLookupField = new SP.FieldLookupValue();    
  newLookupField.set_lookupId(impacts[i]);    
  selectedImpacts.push(newLookupField);  
}              
properties['Impacts'] = selectedImpacts;//MULTI VALUE LOOKUP FIELD              

var selectedDepartmentApprovals = [];  
for (var i = 0; i < departments.length; i++)  
{      
  var newLookupField = new SP.FieldLookupValue();      
  newLookupField.set_lookupId(departments[i]);    
  selectedImpacts.push(newLookupField);  
}  
properties['Department_x0020_Approvals'] = selectedDepartmentApprovals//MULTI VALUE LOOKUP FIELD  
           
var ctx = new SP.ClientContext.get_current();  
var web = ctx.get_web();  ctx.load(web);              
var list = web.get_lists().getByTitle('Change Control Requests (New)');  
ctx.load(list);           
var parentFolder = list.get_rootFolder();  
ctx.load(parentFolder);                             
var docSetContentTypeID = "0x0120D520007B4459305E909F40A1D7E88011667252001AF0C6716A90D743A9D81C085D07EC62";  
var docSetContentType = ctx.get_site().get_rootWeb().get_contentTypes().getById(docSetContentTypeID);  
ctx.load(docSetContentType);           
ctx.executeQueryAsync(function () {      
  SP.DocumentSet.DocumentSet.create(ctx, parentFolder, docSetName, docSetContentType.get_id());      
  var docSetFolder = web.getFolderByServerRelativeUrl(parentFolder.get_serverRelativeUrl() + '/' + docSetName);      
  var docSetFolderItem = docSetFolder.get_listItemAllFields();      
  if (properties != null) 
  {    
     for (var property in properties) {      
       if (properties.hasOwnProperty(property) === true) {                
          docSetFolderItem.set_item(property, properties[property]);             
       }         
     }      
  }      
  docSetFolderItem.update();      
  ctx.load(docSetFolderItem);      
  ctx.executeQueryAsync(function () { 
        addChangeControlSuccess(docSetFolderItem); 
        }, requestFailure);
  },requestFailure);            
}        
function addChangeControlSuccess(data)
{  
  console.log(data);
}
function requestFailure(sender,args)
{  
  console.log('Request Failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}

I am currently getting the error: "Object reference not set to an instance of an object on server. The object associated with method GetById."

It is throwing the error on line:

SP.DocumentSet.DocumentSet.create(ctx, parentFolder, docSetName, docSetContentType.get_id());

Any help on what I am doing wrong is greatly appreciated! Thank you so much!

~ Frankie