remove redundant NULL type assignment to endpoint variables

[xianqiliu]

There are some must existing endpoint variables that will never be null, e.g.

private ?DirectDestinations $directDestinations;

/**
* @return DirectDestinations|null
*/
public function getDirectDestinations(): ?DirectDestinations
{
  return $this->directDestinations;
}

thus those redundant null type assignments on them should be removed.