CHECKBOX_GROUP validators not working

[drkhannah]

I'm submitting a

[ ] Bug / Regression
[ ] Feature Request / Proposal

I'm using

NG Dynamic Forms Version: `12.0.0`

[ ] Basic UI
[ ] Bootstrap UI  
[ ] Foundation UI
[ ] Ionic UI
[ ] Kendo UI
[ ] Material  
[ ] NG Bootstrap
[x ] Prime NG

Description

Hello

Thank you for this great library

I have noticed that when i add validators to a CHECKBOX_GROUP they don't work. I want to require at least one checkbox to be checked in a checkbox group.

{
   "id":"COLLECTION_METHOD_UC",
   "label":"Specimen Collection Method",
   "name":"COLLECTION_METHOD_UC",
   "type":"CHECKBOX_GROUP",
   "validators":{
      "required":null
   },
   "errorMessages":{
      "required":"{{ label }} is required."
   },
   "group":[
      {
         "id":"VOIDED_URINE",
         "label":"Voided Urine",
         "name":"VOIDED_URINE",
         "type":"CHECKBOX",
         "value":null
      },
      {
         "id":"RANDOM_VOID",
         "label":"Random Void",
         "name":"RANDOM_VOID",
         "type":"CHECKBOX",
         "value":null
      }
   ]
}

I have tried using validators and groupValidators, but the formgroup is always valid even after i check and uncheck all checkboxes, and no error message shows if no checkboxes are checked

[ticxx]

as far as i know it needs a custom-validator on the group. in this validator can then be iterated over the controls of the group.

export function myCustomValidator(control: AbstractControl): ValidationErrors | null {                    
  let countChecked = 0;
                    Object.keys(group.controls).forEach((key) => {
                        const c: AbstractControl = group.get(key);
                        if (c.value === true) {
                            countChecked++;
                        }
                    });
                    const hasError = countChecked < 1;
    return hasError ? {myCustomValidator: true} : null;
}