Drawning Line Problem useing custom class

hey i want to draw line useing custom class: using System; using UnityEngine;

 public class Drawing
 {
     public static Texture2D lineTex;
 
     public static void DrawLine(Rect rect) { DrawLine(rect, GUI.contentColor, 1.0f); }
     public static void DrawLine(Rect rect, Color color) { DrawLine(rect, color, 1.0f); }
     public static void DrawLine(Rect rect, float width) { DrawLine(rect, GUI.contentColor, width); }
     public static void DrawLine(Rect rect, Color color, float width) { DrawLine(new Vector2(rect.x, rect.y), new Vector2(rect.x + rect.width, rect.y + rect.height), color, width); }
     public static void DrawLine(Vector2 pointA, Vector2 pointB) { DrawLine(pointA, pointB, GUI.contentColor, 1.0f); }
     public static void DrawLine(Vector2 pointA, Vector2 pointB, Color color) { DrawLine(pointA, pointB, color, 1.0f); }
     public static void DrawLine(Vector2 pointA, Vector2 pointB, float width) { DrawLine(pointA, pointB, GUI.contentColor, width); }
     public static void DrawLine(Vector2 pointA, Vector2 pointB, Color color, float width)
     {
         Matrix4x4 matrix = GUI.matrix;
         if (!lineTex) { lineTex = new Texture2D(1, 1); }
 
         Color savedColor = GUI.color;
         GUI.color = color;
         float angle = Vector3.Angle(pointB - pointA, Vector2.right);
         if (pointA.y > pointB.y) { angle = -angle; }
 
         GUIUtility.ScaleAroundPivot(new Vector2((pointB - pointA).magnitude, width), new Vector2(pointA.x, pointA.y + 0.5f));
         GUIUtility.RotateAroundPivot(angle, pointA);
         GUI.DrawTexture(new Rect(pointA.x, pointA.y, 1, 1), lineTex);
         GUI.matrix = matrix;
         GUI.color = savedColor;
     }
 }

and when in my script i use

 Drawing.DrawLine(_temp, sphere[i, j].transform.position, Color.black);

i got errors:

NullReferenceException: Object reference not set to an instance of an object UnityEngine.GUI.DrawTexture (Rect position, UnityEngine.Texture image, ScaleMode scaleMode, Boolean alphaBlend, Single imageAspect) (at C:/BuildAgent/work/812c4f5049264fad/Runtime/ExportGenerated/Editor/GUI.cs:155) UnityEngine.GUI.DrawTexture (Rect position, UnityEngine.Texture image) (at C:/BuildAgent/work/812c4f5049264fad/Runtime/ExportGenerated/Editor/GUI.cs:152) Drawing.DrawLine (Vector2 pointA, Vector2 pointB, Color color, Single width) (at Assets/Drawing.cs:67) Drawing.DrawLine (Vector2 pointA, Vector2 pointB, Color color) (at Assets/Drawing.cs:30) Main.OnEnter (System.String name) (at Assets/Main.cs:123) UnityEngine.GameObject:SendMessage(String, Object) focus:OnMouseDown() (at Assets/focus.cs:7) UnityEngine.SendMouseEvents:DoSendMouseEvents(Int32, Int32)