spectreconsole/spectre.console · error · ArgumentNullException

Value cannot be null. (Parameter 'value')

Error message

Value cannot be null. (Parameter 'value')

What it means

The TableColumn.Header setter requires a non-null IRenderable. The setter null-coalesces with 'throw new ArgumentNullException(nameof(value))', so assigning null throws immediately. This guards downstream rendering from null-dereference when laying out the header.

Source

Thrown at src/Spectre.Console/Widgets/Table/TableColumn.cs:24

public sealed class TableColumn : IColumn
{
    private IRenderable _header = null!;
    private IRenderable? _footer;

    /// <summary>
    /// Gets or sets the column header.
    /// </summary>
    public IRenderable Header
    {
        get => _header;
        set
        {
            if (value is TableCell cell && cell.ColumnSpan > 1)
            {
                throw new InvalidOperationException("Column spanning is not supported in table header rows.");
            }

            _header = value ?? throw new ArgumentNullException(nameof(value));
        }
    }

    /// <summary>
    /// Gets or sets the column footer.
    /// </summary>
    public IRenderable? Footer
    {
        get => _footer;
        set
        {
            if (value is TableCell cell && cell.ColumnSpan > 1)
            {
                throw new InvalidOperationException("Column spanning is not supported in table footer rows.");
            }

            _footer = value;
        }

View on GitHub (pinned to 0acc92fada)

Solutions

1. Null-coalesce before assignment: column.Header = maybeNull ?? new Markup(string.Empty).
2. Validate with ArgumentNullException.ThrowIfNull(value) at the caller boundary.
3. Use Markup.Empty or new Markup(string.Empty) as a sentinel instead of null.

Example fix

// before
column.Header = headerRenderable; // headerRenderable may be null

// after
column.Header = headerRenderable ?? new Markup(string.Empty);

ArgumentNullException.ThrowIfNull(value);
column.Header = value ?? new Markup(string.Empty);

When it happens

Trigger: column.Header = null; new TableColumn((IRenderable)null); or assigning a nullable IRenderable variable (IRenderable?) that happens to be null.

Common situations: A factory/builder returning null for an absent header; a nullable reference passed without a null check; clearing a header by assigning null instead of an empty Markup; deserialized data yielding null rendered as header.

Related errors

• Value cannot be null. (Parameter 'header')
• Value cannot be null. (Parameter 'text')
• Column spanning is not supported in table header rows.
• Column spanning is not supported in table {rowType} rows.
• Table row index cannot be negative.

AI-assisted analysis of spectreconsole/spectre.console@0acc92fada (2026-08-13). Data as JSON: /api/errors/9f52ed6cfda76939. Report an issue: GitHub.