title: Attempt to call function 'get_position' in base 'null instance' on a null instance. ERROR
body: <p>I am trying to create a topdown shooter with a player and a bullet on a separate scene. But whenever I run the game it says </p>
  
  <blockquote>
    <p>Attempt to call function 'get_position' in base 'null instance' on a null instance.</p>
  </blockquote>
  
  <p>BTW I am new to Godot.<br>
  The problem seems to be in this function:</p>
  
  <pre><code>const SPEED = 300
  var bullet = preload("res://Mini-Scenes/Bullet.tscn")
  
  func shoot():
      var b = bullet.instance()
      add_child(b)
      b.set_position(position)
      b.move_and_slide(Vector2(1, 0).rotated(rotation) * SPEED)
  </code></pre>
  
  <p>And I also don't think that I understand how instancing works,<br>
  so my questions are:</p>
  
  <ol>
  <li>How does <em>Instancing</em> work?</li>
  <li>What makes the above function fail?</li>
  </ol>