I'm unable to clear a variable that is used in multiple scripts.

Context is I watched a "drag and drop" tutorial and everything is great. Except for one thing. When I drag the object onto another object, which I called a "slot", the slot takes the dragged object's text name and I set a variable called cmdname and set it to the text. I run the cmdname as a coroutine afterward.

What I'm unable to do is when I drag the object off of the slot, the cmdname remains set on the previous dragged object's text. I want to clear the variable so that when the slot is emptied it doesn't run anything.

CommandSlot script that sets the cmdname:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.EventSystems;
 
 #pragma warning disable 618, 649
 namespace UnityStandardAssets.Characters.FirstPerson {
 
 public class CommandSlot_1 : MonoBehaviour, IDropHandler
 {
     public GameObject botInsMenu;
     public Bot_Ins_Menu botInsMenuScr;
     //public bool onSlot = false;
     public string cmdname;
 
 
 
     private void Start() {
         botInsMenuScr = botInsMenu.GetComponent<Bot_Ins_Menu>();
     }
 
 
 
     public void OnDrop(PointerEventData eventData) {
         Debug.Log("OnDrop");
         if (eventData.pointerDrag != null) {
             eventData.pointerDrag.GetComponent<RectTransform>().anchoredPosition = GetComponent<RectTransform>().anchoredPosition;
             cmdname = eventData.pointerDrag.name;
 
             //botInsMenuScr.funcs.Add("Move10UnitsBack");
             //botInsMenuScr.funcs.Add("Jump");
         } 
     }
 }
 }

How can I check if the slot is emptied so I can set my cmdname to null or something?