Unity-Technologies/UnityCsReference · error · ArgumentException

columns are no allowed to be null

Error message

columns are no allowed to be null

What it means

Thrown by the MultiColumnHeaderState constructor when the columns array argument is null. A header state with no column definitions cannot render or sort anything, so null is rejected at construction.

Source

Thrown at Editor/Mono/GUI/TreeView/MultiColumnHeaderState.cs:75

                return;
            }

#pragma warning disable UA2001 // The Banned API Analyzer produces compile errors for any new Linq code. This pre-existing usage has been suppressed, but should be rewritten if possible.
            destination.m_VisibleColumns = source.m_VisibleColumns.ToArray();
#pragma warning restore UA2001
            destination.m_SortedColumns = new List<int>(source.m_SortedColumns);

            for (int i = 0; i < destination.m_Columns.Length; ++i)
            {
                destination.m_Columns[i].width = source.m_Columns[i].width;
                destination.m_Columns[i].sortedAscending = source.m_Columns[i].sortedAscending;
            }
        }

        public MultiColumnHeaderState(Column[] columns)
        {
            if (columns == null)
                throw new ArgumentException("columns are no allowed to be null", "columns");
            if (columns.Length == 0)
                throw new ArgumentException("columns array should at least have one column: it is empty", "columns");

            m_Columns = columns;
            m_SortedColumns = new List<int>();

            // Default to all visible
            m_VisibleColumns = new int[m_Columns.Length];
            for (int i = 0; i < m_Columns.Length; ++i)
                m_VisibleColumns[i] = i;
        }

        public int sortedColumnIndex
        {
            get
            {
                return m_SortedColumns.Count > 0 ? m_SortedColumns[0] : -1;
            }

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Always pass a non-null Column[]; use an empty-safe builder that guarantees at least one column.
2. If no columns are applicable, avoid constructing the state at all rather than passing null.
3. Null-coalesce at the call site: columns ?? throw new InvalidOperationException("no columns defined").

Example fix

// before
var st = new MultiColumnHeaderState(BuildColumns()); // may be null

// after
Column[] cols = BuildColumns() ?? throw new InvalidOperationException("No columns defined");
var st = new MultiColumnHeaderState(cols);

if (columns == null) throw new ArgumentNullException(nameof(columns)); // or supply defaults

static bool HasColumns(Column[] c) => c != null && c.Length > 0;

When it happens

Trigger: Constructing 'new MultiColumnHeaderState(null)'; passing a column-builder method that returned null on failure.

Common situations: Dynamic column generation that returns null when no columns are applicable; deserialization helpers that yield null for empty definitions.

Related errors

• MultiColumnHeader state is not allowed to be null
• columnIndices
• sortAscending
• visibleColumns should not be set to null
• Input arrays should have same length

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/a5383ebd1687aaa2. Report an issue: GitHub.