Unity-Technologies/UnityCsReference · error · ArgumentException

Invalid list: cannot be null

Error message

Invalid list: cannot be null

What it means

Thrown by TreeViewControlDataSource.SearchFullTree when the result list argument is null. The method writes matching items into the provided list; a null list has no capacity to receive results.

Source

Thrown at Editor/Mono/GUI/TreeView/TreeViewControl/TreeViewControlDataSource.cs:77

                }

                // Rows
                m_Rows = m_Owner.BuildRows(m_RootItem);
                if (m_Rows == null)
                    throw new NullReferenceException("RefreshRows should set valid list of rows.");

                // Custom row rects
                if (m_Owner.m_OverriddenMethods.hasGetCustomRowHeight)
                    m_Owner.m_GUI.RefreshRowRects(m_Rows);
            }

            public void SearchFullTree(string search, List<TreeViewItem<TIdentifier>> result)
            {
                if (string.IsNullOrEmpty(search))
                    throw new ArgumentException("Invalid search: cannot be null or empty", "search");

                if (result == null)
                    throw new ArgumentException("Invalid list: cannot be null", "result");

                var stack = new Stack<TreeViewItem<TIdentifier>>();
                stack.Push(m_RootItem);
                while (stack.Count > 0)
                {
                    TreeViewItem<TIdentifier> current = stack.Pop();
                    if (current.children != null)
                    {
                        foreach (var child in current.children)
                        {
                            if (child != null)
                            {
                                if (m_Owner.DoesItemMatchSearch(child, search))
                                    result.Add(child);

                                stack.Push(child);
                            }
                        }

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Allocate the results list before calling: var results = new List<TreeViewItem<TIdentifier>>();
2. Initialize the cached results field at declaration or in OnEnable.
3. Add a null guard that allocates on demand.

Example fix

// before
dataSource.SearchFullTree(search, m_Results); // m_Results is null

// after
m_Results = m_Results ?? new List<TreeViewItem<TIdentifier>>();
dataSource.SearchFullTree(search, m_Results);

result = result ?? new List<TreeViewItem<TIdentifier>>();
dataSource.SearchFullTree(search, result);

When it happens

Trigger: Calling SearchFullTree(search, null); passing a list field that was never initialized; a prior code path setting the result reference to null.

Common situations: Custom search invocation that forgets to allocate the results list; refactoring that moved allocation after the call.

Related errors

• Invalid list: cannot be null
• Invalid TreeViewState: it is null
• root is null
• rows is null
• Invalid search: cannot be null or empty

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/772d05cccbb9efc9. Report an issue: GitHub.