code: func (d *ResourceDiff) GetOkExists(key string) (interface{}, bool) {
  	r := d.get(strings.Split(key, "."), "newDiff")
  	exists := r.Exists && !r.Computed
  	return r.Value, exists
  }
docs: // GetOkExists functions the same way as GetOkExists within ResourceData, but
  // it also checks the new diff levels to provide data consistent with the
  // current state of the customized diff.
  //
  // This is nearly the same function as GetOk, yet it does not check
  // for the zero value of the attribute's type. This allows for attributes
  // without a default, to fully check for a literal assignment, regardless
  // of the zero-value for that type.