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

NullReferenceException: Object reference not set to an instance of an object LampStateMachine.YellowState () (at Assets/Scripts/LampStateMachine.cs:56) LampStateMachine.Update () (at Assets/Scripts/LampStateMachine.cs:32)

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Lamp : MonoBehaviour {
 
     [SerializeField] private float greenLight = 5.0f;
     [SerializeField] private float yellowLight = 5.0f;
     [SerializeField] private float redLight = 5.0f;
 
     private float timePassed;
 
     void Start()
     {
         ResetTimeSinceLastTransition();
         GetComponent<Renderer>().material.color = Color.gray;
     }
 
     void Update()
     {
         timePassed += Time.deltaTime;
     }
 
     public float GetTime()
     {
         return timePassed;
     }
 
 
     public void ResetTimeSinceLastTransition()
     {
         timePassed = 5.0f;
     }
     public float GetRedTime()
     {
         return redLight;
     }
 
     public float GetYellowTime()
     {
         return yellowLight;
     }
 
     public float GetGreenTime()
     {
         return greenLight;
     }
 }

This is my state machine, that holds the error. I can't seem to figure out how to fix this any ideas? Also the first script is placed on the lamp it self, the second script is placed on a empty game object.

 using System;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class LampStateMachine : MonoBehaviour {
 
 
     private Lamp target;
     private TrafficStates curState = TrafficStates.redLight;
     private Dictionary<TrafficStates, Action> fsm = new Dictionary<TrafficStates, Action>();
 
 
     void Start()
     {
        
         GetComponent<Lamp>();
      
         fsm.Add(TrafficStates.redLight, new Action(RedState));
         fsm.Add(TrafficStates.yellowLight, new Action(YellowState));
         fsm.Add(TrafficStates.greenLight, new Action(GreenState));
       
         SetState(TrafficStates.redLight);
         SetState(TrafficStates.greenLight);
         SetState(TrafficStates.yellowLight);
 
     }
 
 
     void Update()
     {
         fsm[curState].Invoke();
     }
 
     enum TrafficStates
     {
         greenLight,
         yellowLight,
         redLight
     }
  
     void RedState()
     {
         if (target.GetRedTime() > target.GetTime())
         {
             GameObject yellowObj = GameObject.Find("YellowLight");
 
             yellowObj.GetComponent<Renderer>().material.color = Color.yellow;
 
             SetState(TrafficStates.yellowLight);
         }
     }
   
     void YellowState()
     {
         if (target.GetYellowTime() > target.GetTime())
         {
             GameObject greenObj = GameObject.Find("GreenLight");
 
             greenObj.GetComponent<Renderer>().material.color = Color.green;
 
             SetState(TrafficStates.greenLight);
         }
 
     }
 
     void BlinkingYellowState()
     {
 
     }
 
     void GreenState()
     {
         if (target.GetGreenTime() > target.GetTime())
         {
             GameObject redObj = GameObject.Find("RedLight");
 
             redObj.GetComponent<Renderer>().material.color = Color.red;
 
             SetState(TrafficStates.redLight);
         }
     }
 
 
     void SetState(TrafficStates newState)
     {
         curState = newState;
     }
 }

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