Reversing animation nullpointerexception

First off I am a newbie to programming and gaming development, so thank you in advance for your help and patience!

I am trying to make my door reverse its opening animation but I cannot figure it out for the life of me. I keep getting a nullreferenceexception every time I try. My hierarchy is as follows:

 Door System
      -door_left(cube with opening animation)
      -door_right(cube with opening animation)
      -door_trigger(cube with no mesh set to trigger)

the code is as follows:

 using UnityEngine;
 using System.Collections;
 
 public class DoorHandler : MonoBehaviour {
     public Object Door1;
     public Object Door2;
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void OnTriggerEnter (Collider other) {
     Do_Door_Open (Door1);
     if(Door2 != null){
     Do_Door_Open (Door2);
         }
     }
     
     void OnTriggerExit (Collider other){
     Do_Door_Close (Door1);
     if(Door2 != null){
     Do_Door_Close (Door2);
         }
     
     }
     
     void Do_Door_Open(Object door_to_open){
     Object doorObject = door_to_open != null ? door_to_open : gameObject;
     GameObject open_door_target = doorObject as GameObject;
     open_door_target.animation.Play ();
     }
     
     void Do_Door_Close(Object door_to_close){
     Object doorObject = door_to_close != null ? door_to_close : gameObject;
     GameObject close_door_target = doorObject as GameObject;
         AnimationState anim = close_door_target.animation[close_door_target.animation.name];
         anim.speed = -1.0f;
         anim.time = anim.length;
     close_door_target.animation.Play ();
     }
     
 }

Is there perhaps a better way to going about doing this? Any help would be appreciated!