NullReferenceException: Object Reference not set to an instance of an object

I am making a 2D game in the style of pac-man. I am using a script to place "dots" in the scene (called pacdot in my script). This script is attached to a gameobect called placer which moves round the scene, placing the dots. However as my game contains a maze and therefor I have a ray-casting function that returns a boolean value based on weather the placer game object is in contact with the collider from the maze. If false is returned by the function then no dots are placed and instead the placer moves to the next location. My game contains waypoints. These waypoints are also detected by the raycasting function, however I want dots to be placed over these invisible waypoints. To do this i have given all my waypoints the tag of "Waypoint". I then detect in the ray cast function weather i have detected a waypoint, and if so the function still returns true. I am receiving the error as shown in the title however for line 16 and i do not understand what i am doing wrong. Any help would be really appreciated. :)

using UnityEngine; using System.Collections;

public class Place : MonoBehaviour {

 public GameObject pacdot;

 // Use this for initialization
 void Start () {
 }

 bool valid(Vector2 dir) {
     Vector2 pos = transform.position;
     
     RaycastHit2D hit = Physics2D.Linecast (pos, pos);
     if (hit.collider.gameObject.tag != "Waypoint")
         return (hit.collider == GetComponent<Collider2D> ());
     else return(true);
     
 }

 // Update is called once per frame
 void FixedUpdate () {
     if (valid(Vector2.right)) {
         if (transform.position.y > 1) {
             if (transform.position.x < 28)
                 Instantiate (pacdot, new Vector2 (transform.position.x, transform.position.y), Quaternion.identity);
             transform.Translate (1, 0, 0);
             if (transform.position.x > 28)
                 transform.Translate (-28, -1, 0);
         }
     }    
     if (valid (Vector2.right) == false) {
         transform.Translate (1, 0, 0);
 }
 }

}