code: func (d *ResourceDiff) GetOk(key string) (interface{}, bool) {
  	r := d.get(strings.Split(key, "."), "newDiff")
  	exists := r.Exists && !r.Computed
  	if exists {
  		// If it exists, we also want to verify it is not the zero-value.
  		value := r.Value
  		zero := r.Schema.Type.Zero()
  
  		if eq, ok := value.(Equal); ok {
  			exists = !eq.Equal(zero)
  		} else {
  			exists = !reflect.DeepEqual(value, zero)
  		}
  	}
  
  	return r.Value, exists
  }
docs: // GetOk functions the same way as ResourceData.GetOk, but it also checks the
  // new diff levels to provide data consistent with the current state of the
  // customized diff.