Keep getting this error on different Text boxes. Any help would be appreciated!

NullReferenceException: Object reference not set to an instance of an object textHolder+c__Iterator1.MoveNext () (at Assets/Script/textHolder.cs:27) UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator) textHolder:Start() (at Assets/Script/textHolder.cs:19)

The code:

using UnityEngine; using System.Collections; using UnityEngine.UI;

public class textHolder : MonoBehaviour {

 public string talking;
 private TextManager TMan;

 public float speed = 0.1f;
 //public string fullText;
 //private string currentText = "";

 public string[] talkingLines;

 // Use this for initialization
 void Start () {
     TMan = FindObjectOfType <TextManager> ();
     StartCoroutine(ShowText());
 }

 IEnumerator ShowText(){
     for (int i = 0; i < talkingLines.Length; i++) {

         talking = talkingLines[i];

         this.GetComponent<Text> ().text = talking;

         yield return new WaitForSeconds (1);
     }
 }
 
 // Update is called once per framea
 void Update () {
     
 }

 void OnTriggerStay2D (Collider2D other)
 {
     
     if (other.gameObject.name == "Player")
     {    
         if (Input.GetKeyUp (KeyCode.Space)) 
         {
             //TMan.ShowBox (talking);

              if (!TMan.talkingActive)
             
             {
                 TMan.talkingLines = talkingLines;
                 TMan.currentLine = 0;
                 TMan.showTalking ();
             }
         }
     
     }
 }

}