Unity-Technologies/UnityCsReference · error · ArgumentNullException

windowContent

Error message

windowContent

What it means

PopupWindowWithoutFocus.Show throws ArgumentNullException(nameof(windowContent)) when the PopupWindowContent argument is null. The popup requires a content object to render, so a null content is rejected at the boundary rather than opening an empty window.

Source

Thrown at Editor/Mono/GUI/PopupWindowWithoutFocus.cs:29

using Unity.Scripting.LifecycleManagement;

namespace UnityEditor
{
    partial class PopupWindowWithoutFocus : PopupWindow
    {
        [AutoStaticsCleanupOnCodeReload]
        static PopupWindowWithoutFocus s_PopupWindowWithoutFocus;
        bool hasBeenFocused = false;

        public new static void Show(Rect activatorRect, PopupWindowContent windowContent)
        {
            Show(activatorRect, windowContent, null);
        }

        internal new static void Show(Rect activatorRect, PopupWindowContent windowContent, PopupLocation[] locationPriorityOrder)
        {
            if (windowContent == null)
                throw new System.ArgumentNullException(nameof(windowContent));

            if (s_PopupWindowWithoutFocus != null)
            {
                s_PopupWindowWithoutFocus.Close();
                s_PopupWindowWithoutFocus = null;
            }

            if (ShouldShowWindow(activatorRect))
            {
                if (s_PopupWindowWithoutFocus == null)
                    s_PopupWindowWithoutFocus = CreateInstance<PopupWindowWithoutFocus>();

                s_PopupWindowWithoutFocus.Init(activatorRect, windowContent, locationPriorityOrder, ShowMode.PopupMenu, false);
            }
            else
            {
                windowContent.OnClose();
            }

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Return early when content is null instead of calling Show.
2. Ensure the content factory never returns null; provide a fallback content.
3. Null-check at the call site before invoking Show.

Example fix

// before
PopupWindowWithoutFocus.Show(rect, content);
// after
if (content != null)
    PopupWindowWithoutFocus.Show(rect, content);

if (windowContent != null)
    PopupWindowWithoutFocus.Show(rect, windowContent);

static bool HasContent(PopupWindowContent c) => c != null;

When it happens

Trigger: Calling Show with a PopupWindowContent that evaluated to null (a factory returned null, a conditional content path was skipped, or a field was never assigned).

Common situations: Conditional popup content that returns null when there is nothing to show; refactoring that drops the content argument; passing a not-yet-constructed content.

Related errors

• Parameter selected must be of type System.Enum
• Calling GUISkin.current outside OnGUI. This might break the
• Cannot select range when not in multi select mode.
• The path is null
• prefabInstanceRoots

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/482c1d2f2979baa5. Report an issue: GitHub.