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

So I've got a public class, and I'm trying to create an array of this class and pass it to a function to initialize it, but I get this error on the first line, during runtime.

NullReferenceException: Object reference not set to an instance of an object BoardDetector.initialize_board_state (.boardstate[] BoardState) (at Assets/Scripts/BoardDetector.cs:43) BoardDetector.Start () (at Assets/Scripts/BoardDetector.cs:27)

 using UnityEngine;
 using System.Collections;
 using System;
 
 
 [System.Serializable]
 public class boardstate
 {
     public string name;
     public bool active;
     public float x;
     public float z;
 }
 
 
 
 public class BoardDetector : MonoBehaviour {
     private RaycastHit hit;
     private Ray ray;
 
 
     public boardstate[] BoardState;
     public float[] point;
     // Use this for initialization
     void Start () {
         BoardState = new boardstate[32];
         initialize_board_state (BoardState);
     }
     
     
     
     // Update is called once per frame
     void Update () {
         ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         if (Physics.Raycast (ray, out hit) && Input.GetMouseButtonUp(0)) {
             point [0] = hit.point.x >= 0 ? (float)((int)hit.point.x) + 0.5f : (float)((int)hit.point.x) - 0.5f;
             point [1] = hit.point.z >= 0 ? (float)((int)hit.point.z) + 0.5f : (float)((int)hit.point.z) - 0.5f;
         }        
     }
     void initialize_board_state(boardstate[] BoardState)
     {
         for (int i = 0; i < 8; i++) {
             BoardState[i].name = "wp";
             BoardState[i].active = true;
             BoardState[i].x = -3.5f + (float)i;
             BoardState[i].z = -2.5f;
         }
         for (int i = 8; i < 10; i++) {
             BoardState [i].name = "wr";
             BoardState [i].active = true;
             BoardState [i].x = -3.5f + (float)(7 * (i - 8));
             BoardState [i].z = -3.5f;
         }
         for (int i = 10; i < 12; i++) {
             BoardState [i].name = "wk";
             BoardState [i].active = true;
             BoardState [i].x = -2.5f + (float)(5 * (i - 10));
             BoardState [i].z = -3.5f;
         }
         for (int i = 12; i < 14; i++) {
             BoardState [i].name = "wb";
             BoardState [i].active = true;
             BoardState [i].x = -1.5f + (float)(3 * (i - 12));
             BoardState [i].z = -3.5f;
         }
         BoardState [14].name = "wq";
         BoardState [14].active = true;
         BoardState [14].x = -0.5f;
         BoardState [14].z = -3.5f;
         
         BoardState [15].name = "wg";
         BoardState [15].active = true;
         BoardState [15].x =  0.5f;
         BoardState [15].z = -3.5f;
         
         for (int i = 16; i < 24; i++) {
             BoardState [i].name = "bp";
             BoardState [i].active = true;
             BoardState [i].x = -3.5f + (float)i - 16.0f;
             BoardState [i].z = 2.5f;
         }
         
         for (int i = 24; i < 26; i++) {
             BoardState [i].name = "br";
             BoardState [i].active = true;
             BoardState [i].x = -3.5f + (float)(7 * (i - 24));
             BoardState [i].z =  3.5f;
         }
         for (int i = 26; i < 28; i++) {
             BoardState [i].name = "bk";
             BoardState [i].active = true;
             BoardState [i].x = -2.5f + (float)(5 * (i - 10));
             BoardState [i].z =  3.5f;
         }
         for (int i = 28; i < 30; i++) {
             BoardState [i].name = "bb";
             BoardState [i].active = true;
             BoardState [i].x = -1.5f + (float)(3 * (i - 12));
             BoardState [i].z =  3.5f;
         }
         BoardState [30].name = "bq";
         BoardState [30].active = true;
         BoardState [30].x =  0.5f;
         BoardState [30].z =  3.5f;
         
         BoardState [31].name = "bg";
         BoardState [31].active = true;
         BoardState [31].x = -0.5f;
         BoardState [31].z =  3.5f;
         
         
     }
 }