Null Reference Exception error

Hi guys

new to C# (Kinda) Getting a null reference error on Line 22 (ill post the full code below, but you can see the error and line 22 in the image, where the error is pointing to. any ideas on how to fix? Its baffled me.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class SF_PatrolEnemyMove : SF_Enemy_Move 
 {
     //list to hold waypoinmts for movement
     public List<Vector3> mLS_V3_Waypoints = new List<Vector3>();
 
     //Holds indec in mLS_V3_Waypoints that is current target
     private int mIN_TargetIndex = 0;
 
     //Holds all colliders that the enemy vision collider hits
     public List<Collider> mHitTargets = new List<Collider>();
 
 
     // Use this for initialization
     void Start () 
     {
         base.Start ();
         mST_State = "patrol";
         mTM_StateText.text = mST_State;
         HP = 20;
         Defence = 8;
     }
     //initialise patrol path for enemy
     public void StartPatrol(List<Vector3> vLS_V3_Waypoints, float vFL_Speed)
     {
         mFL_Speed = vFL_Speed;
         foreach(Vector3 tV3_Waypoint in vLS_V3_Waypoints)
         {
             mLS_V3_Waypoints.Add (tV3_Waypoint);
         }
         mST_State = "patrol";
         mTM_StateText = GetComponentInChildren<TextMesh> ();
         mTM_StateText.text = mST_State;
         mV3_TargetPos = mLS_V3_Waypoints [0];
     }
 
     //method to switch states of enemy by triggers
     protected override void Triggers()
     {
         if(mMB_PCScript.ST_State == "carry" && mST_State != "flee")
         {//change to flee state if PC is in carry
             mST_State = "flee";
             mTM_StateText.text = mST_State;
         }
         if(mMB_PCScript.ST_State == "walk" && mST_State == "flee")
         {//change to chase state if PC is in walk state and NPC was just fleeing
             mST_State = "chase";
             mTM_StateText.text  = mST_State;
         }
         if(mST_State == "chase" && mFL_TargetDistance > 10F)
         { //change to roam state id PC is outside of a certain range
             mST_State = "patrol";
             mTM_StateText.text = mST_State;
         }
     }
 
     //---------------TRIGGERS------------
 
     void OnTriggerEnter(Collider vCL_Spotted)
     {
         //if collider is not already in mHitTargets List and not
         //tagged ignore like our waypoint markers
         if(mHitTargets.Find(x => x == vCL_Spotted) == null && vCL_Spotted.transform.tag != "ignore")
         {
             mHitTargets.Add (vCL_Spotted);
         }
         //createt a collider to hold closest object we collide with
         Collider tCL_Closest = null;
 
         //variable to store closest distance
         float mFL_ClosestDis = 99;
 
         //loop through all colliders in list
 //        foreach(Collider col in mHitTargets)
 //        {
 //            if(col.transform!=null)
 //            {
 //                //if distance between object collided with is less than previous distance of currrenly closest object then update
 //                if(Vector3.Distance (col.transform.position, transform.position) < mFL_ClosestDis)
 //                {
 //                    mFL_ClosestDis = Vector3.Distance(col.transform.position, transform.position);
 //                    tCL_Closest = col;
 //                }
 //            }
 //        }
 
         //if closest object is not null this only causes problems if object collided with is tagged ignore
         if(tCL_Closest != null)
         {
             if(tCL_Closest.gameObject.tag == "Player")
             {//if player is closest object then chase
                 mST_State = "chase";
                 mTM_StateText.text = "!";
                 mTM_StateText.color = Color.red;
             }
         }
         tCL_Closest = null;
         mFL_ClosestDis = 99;
     }
 
     //Method called on the frame an objct stops colliding with the enemy
     void OnTriggerExit(Collider vCL_Spotted)
     {
         mHitTargets.Remove (vCL_Spotted);
     }
 
     //Our method to called state movement methods
     protected override void Move()
     {
         base.Move ();
 
         if (!mLM_LevelManager.isPaused())
         {
             //resolve game states
             switch (mST_State)
             {//Call appropriate methods to deal with movement in current state
             case "patrol": Patrol(); break;
             }
         }
     }
 
     //method defining movement in patrol state
     void Patrol()
     {
         if (Vector3.Distance (mV3_CurrentPos, mGO_Character.transform.position) > 0.1F)
         {
             mBL_Moving = true;
             //find the vector pointing from our position to the target
             Vector3 tV3_Direction = (mV3_CurrentPos - mGO_Character.transform.position).normalized;
 
             //create the rotation we need to be in to look at the target
             Quaternion tQT_Rotation = Quaternion.LookRotation(tV3_Direction);
             mBL_Moving = true;
             //Rotate gradually to target instead of instantly
             mGO_Character.transform.rotation = Quaternion.Lerp (mGO_Character.transform.rotation,
                                                                 tQT_Rotation, 15 * Time.deltaTime);
             mGO_Character.transform.position = Vector3.MoveTowards (mGO_Character.transform.position,
                                                                     mV3_CurrentPos, mFL_Speed * Time.deltaTime);
         }
         else if(Vector3.Distance (mV3_TargetPos, mGO_Character.transform.position) > 0.1F)
         {
             ChooseNextPosition();
         }
         else
         {
             transform.position = mV3_TargetPos;
         }
     }
 
     //Method to set movement target for all states
     protected override void SetTarget()
     {
         //patrol state set target
         if (mST_State == "patrol")
         {
             if(mIN_TargetIndex == 0)
             {
                 SetPatrolTarget(mLS_V3_Waypoints[0]);
             }
             else
             {
                 SetPatrolTarget(mLS_V3_Waypoints[mIN_TargetIndex]);
             }
             ComputeTargetDistance();
 
             //if the NPC has reached the target waypoint choose another
             if (mFL_TargetDistance < 0.1F)
             {
                 if(mIN_TargetIndex == (mLS_V3_Waypoints.Count - 1))
                 {//if reached end of list then choose the first waypoint again
                     SetPatrolTarget(mLS_V3_Waypoints[0]);
                     mIN_TargetIndex = 0; //update index
                 }
                 else
                 {
                     SetPatrolTarget(mLS_V3_Waypoints[mIN_TargetIndex + 1]);
                     mIN_TargetIndex++; //update index
                 }
             }
         }
         else
         {//all other states use base class settarget()
             base.SetTarget();
         }
 
     }//--------------
     void SetPatrolTarget(Vector3 vV3_Pos)
     {
         mV3_TargetPos = vV3_Pos;
     }
     
 }