Unexpected NullReferenceException

I am working on a game using a class library I made (Soldiers.dll) where I can place a SoldierObject script on a GameObject to make it behave like a soldier. However, I have had constant problems with an unexpected NullReferenceException and I quite frankly cannot understand what's going on here.

Here is the setup of my scene.

I have two GameObjects: Soldier1 and Soldier2 each having a SoldierObject script on them: The SoldierObject script looks like this:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using Soldiers;
 
 public class SoldierObject : MonoBehaviour
 {
 
     public WeaponObject weapon;
     public ArmorObject armor;
     public string Name = "Unknown";
     public int Hp = 1;
     public uint Strength = 0;
     public uint Agility = 0;
 
     public Soldier soldier;
 
     void OnEnable()
     {
         soldier = new Soldier(Name, weapon.weapon, armor.armor, Hp, Strength, Agility);
     }
 
     void Update ()
     {
         Name = soldier.name();
         weapon.weapon = soldier.wep();
         armor.armor = soldier.arm();
         Hp = soldier.hp();
         Strength = soldier.strength();
         Agility = soldier.agi();
     }
 }
 

So far everything works. However, things start going awry when the AttackOther script comes into play which is placed on Soldier1:

The script looks like this:

 using System.Collections;
 using System.Collections.Generic;
 using System;
 using UnityEngine;
 using Soldiers;
 
 public class AttackOther : MonoBehaviour {
 
     public SoldierObject other;
     public SoldierObject self;
 
     private bool attacked = false;
     
     // Update is called once per frame
     void Update () {
         if(Time.time >= 3 && !attacked)
         {
             attacked = true;
             self.soldier.attack(other.soldier, 1);
         }
     }
 }

The attack function is a public function of the Soldier class:

 public SoldierState attack(Soldier other, double mult)
         {
             int atk = (int)Math.Round(this.wep().power() * mult) + (int)this.strength();
             return other.hp((int)(other.hp() - Math.Abs(other.arm().defense() - atk))) > 0 ? other.state : SoldierState.dead;
         }

At this time whenever

 self.soldier.attack(other.soldier, 1);

is executed I get this error:

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

Soldiers.Soldier.attack (Soldiers.Soldier other, Double mult) (at C:/Users/AdminBenni/documents/visual studio 2017/Projects/Soldiers/Soldiers/Class1.cs:160)

AttackOther.Update () (at Assets/Scripts/AttackOther.cs:19)

This makes me confused because as far as I know everything I'm referencing actually exists.

All help appreciated :)

 if (somefield == null)
 {
     Debug.Log("Somefield is null!");
 }