.data serialize and deserialize work in editor but not in build

Hello world!

First and foremost, please assume I'm a cavesman. I tried to make my script as simple as possible, because I'm quite the beginner at this, and I'd be ever-so-grateful for a simple, easily comprehensible answer.

So here's the deal : I've created a custom class (ActorData) that I use to store all information pertaining to instantiatable characters in game (the player may create/edit/delete actors at will in a menu).

I then save the current actors in a list that I save in .data format. (tried XML, but couldn't find a tutorial clear and explicit enough for me).

The whole process works flawlessly in the editor, but the list itself, when in a build, simply dosen't get loaded at all! I honestly don't get what's happening.

Here's the problematic code:

 using UnityEngine;
 using System.Collections;
 using System;
 using System.Runtime.Serialization.Formatters.Binary;
 using System.IO;
 using UnityEngine.UI;
 using System.Collections.Generic;
 
 public class ActorSaveAndLoad : MonoBehaviour {
 
     public void SaveActorData (List <ActorData> Data) {
         
         BinaryFormatter bf = new BinaryFormatter ();
         FileStream file = File.Create (Application.dataPath + "/Resources/Data/Object Information/Figurines/FigData.dat");
 
         bf.Serialize (file, Data);
         file.Close ();
     }
 
     public List<ActorData> LoadActorData () {
 
         List<ActorData> data;
 
         if (File.Exists (Application.dataPath + "/Resources/Data/Object Information/Figurines/FigData.dat")){
             BinaryFormatter bf = new BinaryFormatter ();
             FileStream file = File.Open (Application.dataPath + "/Resources/Data/Object Information/Figurines/FigData.dat", FileMode.Open);
             data = (List<ActorData>)bf.Deserialize (file) as List<ActorData>;
             file.Close ();
 
         } else {
             data = null;
 
         }
 
         if (GameObject.Find("TestText").gameObject && data != null) {
             GameObject.Find ("TestText").gameObject.GetComponent<Text> ().text = ("data contains "+data.Count+" objects");
         } else if (GameObject.Find("TestText").gameObject && data == null) {
             GameObject.Find ("TestText").gameObject.GetComponent<Text> ().text = ("data ain't here!");
         }
 
         return data;
     }
 
 }
 
 [Serializable]
 public class ActorData {
 
     public string ActorName;
     public bool IsPlayer;
     public string PlayerName;
     public bool IsHostile;
     public bool UseQuickHP;
     public int MinHP;
     public int MaxHP;
     public string ActorNotes;
     public float ActorSize;
     public string FigModelName;
     public String PedModelName;
 
     public ActorData (string name, bool player, string pName, bool hostile, bool quickHP, int minHP, int maxHP, string notes, float size, string figName, string pedName) {
         ActorName = name;
         IsPlayer = player;
         if (IsPlayer) {
             PlayerName = pName;
         } else {
             PlayerName = null;
         }
         IsHostile = hostile;
         UseQuickHP = quickHP;
         MinHP = minHP;
         MaxHP = maxHP;
         ActorNotes = notes;
         ActorSize = size;
         FigModelName = figName;
         PedModelName = pedName;
     }

in a build, this simply throws a NullReferenceException whenever the list is called by another script.

Does anyone know how to fix this?