null pipe angular 2 returns error when AOT

Question

I have this pipe:

   @Pipe({
  name: 'transformNull'
})

export class TransformNull implements PipeTransform {

  transform(value: any) {
    switch(value){
      case null:
      case undefined:
      case "null":
      case "undefined":
        value = null;
        break;
      default:
        if(typeof(value) == "string"){
          value = value.trim();
        }
        break;
    }
    return value.toString();
  }
}

and this is the html code:

<input type="text" formControlName="chipNumber" autocorrect="off" autocapitalize="off" spellcheck="off" name="chipNumber" class="form-control" id="chipNumber" placeholder="Αριθμός Microchip" [ngModel]="pet.chipNumber | transformNull" (ngModelChange)="pet.chipNumber.value = $event">

When i run on JIT (ng build --prod), the pipe works as it should, when a field has "null" then ngModel returns an empty field from mongo.

When i run ng build --prod --aot then i receive the following error:

TypeError: Cannot create property 'value' on string ''

and here is the aot code:

t.prototype.handleEvent_267 = function(e, t) {
            this.markPathToRootAsCheckOnce();
            var n = !0;
            if (n = this._DefaultValueAccessor_267_3.handleEvent(e, t) && n,
            "ngModelChange" == e) {
                var i = (this.context.pet.chipNumber.value = t) !== !1;
                n = i && n
            }
            return n
        }

funny thing is, in every other page that the pipe exists, it works as it should in aot. Just in this page i get this error. I resolve all routes with a resolver so data is ok, it comes in as it should.

Answer 1

Using this code issue solved:

pet.chipNumber = $event

Instead of:

pet.chipNumber.value = $event