import {Pipe, PipeTransform} from '@angular/core';

@Pipe({
name: 'transformNull'
 })

export class TransformNull implements PipeTransform {

transform(value) {
if (value == null) {
  return null;
 }
}

[ngModel]="user.extraInfo | transformNull" (ngModelChange)="user.extraInfo.value=$event"

Cannot set property 'value' of undefined TypeError: Cannot set property 'value' of undefined