Object reference not set to an instance of an object

Hi, I have had a working script in JS that controls my character, but I am trying to re-write it in C#.

It does not error until I try to jump using the playerOneJumpTime routine, then I get the object reference error.

I have gone through the code over and over and I cant see why the jump coroutine is causing problems?

Please can someone help as I cant see the woods for the trees anymore.

 using UnityEngine;
 using System.Collections;
 
     [System.Serializable]
     public class playerOneAttributes
     {
     public string playerOneName = "Player 1";                //Players name in game, can be changed
     public int playerOneHealth = 100;                        //Players Total Current Health
     public int playerOneRangePower = 100;                    //Players range damage (ie. fireballs, arrows)
     public int playerOneMagicDamage = 100;                    //Players spell damage from potions
     public int playerOneMeleeDamage = 100;                    //Players melee damage
     public int playerOneDefense = 10;                        //Players Defense
     public float playerOneMoveSpeed = 100;                    //Players movement speed
     public int playerOneXP = 0;                                //Players XP
     }
 
     [System.Serializable]
     public class playerOnelevelUpMultipliers
     {
         public float playerOneHealthMultiplier = 1.5f;          //Players health multplier upon level up
         public float playerOneRangeMultiplier = 1.5f;           //Players range power multplier upon level up
         public float playerOneMagicMultiplier = 1.5f;           //Players magic power multplier upon level up
         public float playerOneMeleeMultiplier = 1.5f;           //Players melee power multplier upon level up
         public float playerOneDefenseMultiplier = 1.5f;         //Players defense multplier upon level up
     }
 
     [System.Serializable]
     public class playerOneControls
     {
         public string playerOneControlUp = "w";                    //Player Controls (re-mappable)
         public string playerOneControlDown = "s";                //Player Controls (re-mappable)
         public string playerOneControlLeft = "a";                //Player Controls (re-mappable)
         public string playerOneControlRight = "d";                //Player Controls (re-mappable)
         public string playerOneControlJump = ",";                //Player Controls (re-mappable)
         public string playerOneControlAttack = ".";                //Player Controls (re-mappable)
         public string playerOneControlMagic = "/";                //Player Controls (re-mappable)
     }
 
     public class playerOnePhysics
     {
         public float playerOneJumpRate = 1.1f;                    //Players time between jumps
         public float playerOneJumpPower = 5.0f;                    //Players Jump Power
     }
 
     [System.Serializable]
     public class playerOneStatus
     {
         public bool playerOneAlive = true;                        //Is player one alive?
         public bool playerOneIsIt = false;                        //Is player IT?
         public bool playerOneStunned = false;                   //Is player one stunned?
         public bool playerOnePoisoned = false;                    //Is player one poisoned?
     }
 
     [System.Serializable]
     public class playerOneInventory
     {
         public int playerOnePotionAmount = 0;                    //Magic potion amount
         public int playerOneKeyAmount = 0;                        //Number of keys held
         public bool playerOnePowerUpOne = false;                //Extra Shot Power
         public bool playerOnePowerUpTwo = false;                //Extra Melee Power
         public bool playerOnePowerUpThree = false;                //Extra Magic Power
         public bool playerOnePowerUpFour = false;                //Extra Speed
         public bool playerOnePowerUpFive = false;                //Extra Armour
         public bool playerOnePowerUpSix = false;                //Extra Fight Power
         public bool playerOnePowerUpSeven = false;                //Extra XP
     }
 
     public class ScriptPlayerOneManager : MonoBehaviour
     {
 
         public playerOneAttributes playerAttributes;            //These show the variables in the inspector
         public playerOnelevelUpMultipliers levelUpMultipliers;
         public playerOneControls playerControls;
         public playerOnePhysics playerPhysics;
         public playerOneStatus playerStatus;
         public playerOneInventory playerInventory;
         
 
         // Use this for initialization
         void Start()
         {
             rigidbody.freezeRotation = true;                // Prevent the player from falling over due to physics
             StartCoroutine(playerOneJumpTime());
             
         }
 
 
         // Update is called once per frame
         void Update()
             {
             if (Input.GetKey(playerControls.playerOneControlUp))
             {
                 transform.position += new Vector3(0, 0, 0.035f * playerAttributes.playerOneMoveSpeed) * Time.deltaTime;
             }
 
             if (Input.GetKey(playerControls.playerOneControlDown))
             {
                 transform.position -= new Vector3(0, 0, 0.035f * playerAttributes.playerOneMoveSpeed) * Time.deltaTime;
             }
 
             if (Input.GetKey(playerControls.playerOneControlRight))
             {
                 transform.position += new Vector3(0.035f * playerAttributes.playerOneMoveSpeed, 0, 0) * Time.deltaTime;
             }
 
             if (Input.GetKey(playerControls.playerOneControlLeft))
             {
                 transform.position -= new Vector3(0.035f * playerAttributes.playerOneMoveSpeed, 0, 0) * Time.deltaTime;
             }
 
           
         }
 
         IEnumerator playerOneJumpTime()        // This function controls the players jump - makes the player wait to be able to jump again
         {
             while (true)
             {
                 if (Input.GetKeyDown(playerControls.playerOneControlJump))
                 {
                     rigidbody.velocity = new Vector3(0, playerPhysics.playerOneJumpPower, 0);
                     yield return new WaitForSeconds(playerPhysics.playerOneJumpRate);
                 }
                 else
                 {
                     yield return null;
                 }
             }
         }
 
 
     }