Screen pos out of view frustrum, Minimap Cleanup

I made a Minimap, or "Radar" that shows the entire world in my game.

This map can change size depending on what you use for the camSize variable in game. set it to 0 makes the frustrum error appear. Another thing my camera does is that it errors if i dont enter a value for camSize, so if camSize is empty i force the digit 1 to be my camSize, however for a brief second i get another error.

I understand why. My question is, is my scripting ok or should i do something different? Im not an advanced coder so i dont know if i should ignore the errors or find a work around.

If anyone wants to see the code:

 using UnityEngine;
 using System.Collections;
 using System.Text.RegularExpressions;
 
 public class Maps : MonoBehaviour {
 
     public Camera worldMap;
     public bool mapOpen = false;
     private string camSize = "1000";
     public GUISkin customSkin;
     void Start () {
         mapOpen = false;
     }
     void Update(){
         if(Input.GetKeyUp (KeyCode.M)){
             mapOpen = !mapOpen;
         }
 }
     void OnGUI(){
         GUI.skin = customSkin;
         if(camSize == "" || camSize == "."){
             camSize = "1";
         }
         if(mapOpen){
             GUI.Label(new Rect(Screen.width / 2 - 10, Screen.height / 2 - 10, 20, 20),"▲");
             worldMap.rect = new Rect (0, 0, 1, 1);
             camSize = GUI.TextField (new Rect(Screen.width - 50, Screen.height - 20, 50, 20), camSize);
             camSize = Regex.Replace(camSize, @"[^0-9.]", "");
             float temp = float.Parse(camSize);
                 worldMap.orthographicSize = temp;
         }
         if(!mapOpen){
             worldMap.rect = new Rect (0, 0, 0, 0);
             
         }
     }
 }