NullReferenceException

Hi everyone.

I'm trying to write a simple 12 hour timer in C# to be displayed on the canvas. The time itself is displaying, but does not count up because Unity keeps spitting back this error:

NullReferenceException: Object reference not set to an instance of an object timeOfDay.Update () (at Assets/scripts/timeOfDay.cs:28)

The weird thing is, the object on line 28 is declared

 timer.text = time;

and when I build the code inside of MonoDevelop, it returns no errors whatsoever. If i comment out this part, Unity returns the same error but on line 37

 amPM.text = "pm";

and 41

 amPM.text = "am";

As you can see in my full code below, these 3 things are declared, and they are assigned via the inspector.

 using UnityEngine;
 using System.Collections;
 
 using UnityEngine.UI;
 using System;
 
 public class timeOfDay : MonoBehaviour {
 
     float myTimer;
     public Text timer;
     public float modifier;
     TimeSpan t;
     public bool TOD;
     public Text amPM;
 
 
     void Update () 
     {
 
         t = TimeSpan.FromSeconds (Time.time * modifier) + new TimeSpan (4, 0, 0);
         
         if (t.Hours >= 12) {
             t -= new TimeSpan (12, 0, 0);
         }
 
         string time = string.Format("{0:00}:{1:00}", t.Hours, t.Minutes);
         Debug.Log (time);
         timer.text = time;
         
         if (t.Hours >=11 && t.Minutes >= 59) 
         {
             TOD =! TOD;
         }
         
         if (TOD == false) 
         {
             amPM.text = "pm";
         }
         else 
         {
             amPM.text = "am";
         }
     }
 }
 

Thanks in advance for your help, really not sure what I'm doing wrong.