How do you access the Scripts, Functions, and Bools within an array of GameObjects?

I'm trying to develop a system that allows me to switch out menus when the player presses a button. I already have a HideMenu and ShowMenu function in a class on each menu GameObject, each attached to a button. Whenever these occur, they switch a isShown boolean. However, I want it so that when the player presses another button, it performs HideMenu for any menus for which isShown is active. I can't just use active and not active because I'm tweening them, not disabling them. Each Sliding Menu is its own GameObject, with its own MenuBehavior script.

My idea was this:

1. Declare an array of GameObjects called slideMenus in a separate MenuManager script.

2. In start, assign all GameObjects with the tag 'SlideMenu' into this array.

3. In a SwitchMenu function (called by the buttons), perform a foreach loop for each item in the array.

4. In the loop, if isShown is true, activate the function HideMenu.

Code:

 public class MenuManager : MonoBehaviour {
     
         private GameObject[] slideMenus;
     
         public void Start()
             {
                 slideMenus = GameObject.FindGameObjectsWithTag("SlideMenu");
             }
     
         public void SwitchMenu ()
             {
                 foreach (GameObject menu in slideMenus)
                 {
                     if (menu.GetComponent<MenuBehaviour>().isShown)
                         menu.GetComponent<MenuBehaviour>().HideMenu();
                 }
             }
         }

The code doesn't present any errors, but in practice I get

"NullReferenceException: Object reference not set to an instance of an object MenuManager.SwitchMenu () (at Assets/Scripts/MenuManager.cs:58) UnityEngine.Events.InvokableCall.Invoke (System.Object[] args) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:153) UnityEngine.Events.InvokableCallList.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:630) UnityEngine.Events.UnityEventBase.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:765) UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:53) UnityEngine.UI.Button.Press () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:35) UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:44) UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:52) UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:269) UnityEngine.EventSystems.EventSystem:Update()"

as an error.

Any help would be appreciated.

EDIT: Alternatively, I could do the reverse and make ShowMenu just hide any other menus that are active, but that presents the same kind of problem with accessing the MenuBehaviour of other menus.