spectreconsole/spectre.console · error · ArgumentNullException

Value cannot be null. (Parameter 'children')

Error message

Value cannot be null. (Parameter 'children')

What it means

Thrown by the Rows(IEnumerable<IRenderable>) constructor when the children collection is null. The params overload delegates to this overload and passes the array; a null IEnumerable is rejected. An empty collection is allowed (renders nothing).

Source

Thrown at src/Spectre.Console/Widgets/Rows.cs:28

    /// <inheritdoc/>
    public bool Expand { get; set; }

    /// <summary>
    /// Initializes a new instance of the <see cref="Rows"/> class.
    /// </summary>
    /// <param name="items">The items to render as rows.</param>
    public Rows(params IRenderable[] items)
        : this((IEnumerable<IRenderable>)items)
    {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="Rows"/> class.
    /// </summary>
    /// <param name="children">The items to render as rows.</param>
    public Rows(IEnumerable<IRenderable> children)
    {
        _children = new List<IRenderable>(children ?? throw new ArgumentNullException(nameof(children)));
    }

    /// <inheritdoc/>
    protected override Measurement Measure(RenderOptions options, int maxWidth)
    {
        if (Expand)
        {
            return new Measurement(maxWidth, maxWidth);
        }
        else
        {
            var measurements = _children.Select(c => c.Measure(options, maxWidth)).ToArray();
            if (measurements.Length > 0)
            {
                return new Measurement(
                    measurements.Max(c => c.Min),
                    measurements.Max(c => c.Max));
            }

View on GitHub (pinned to 0acc92fada)

Solutions

1. Pass a non-null collection; use Enumerable.Empty<IRenderable>() for no rows.
2. Coalesce with '?? Array.Empty<IRenderable>()'.
3. Initialize the source collection before constructing Rows.

Example fix

// before
var rows = new Rows(maybeNullList);

// after
var rows = new Rows(maybeNullList ?? Array.Empty<IRenderable>());

children ??= Array.Empty<IRenderable>();
var rows = new Rows(children);

static bool HasValidRowsCollection(IEnumerable<IRenderable>? children) => children is not null;

When it happens

Trigger: Constructing 'new Rows((IEnumerable<IRenderable>)null)' or passing a list variable that is null.

Common situations: A filter/LINQ query that can return null, or a field that was never initialized.

Related errors

• Value cannot be null. (Parameter 'content')
• Value cannot be null. (Parameter 'text')
• Value cannot be null. (Parameter 'title')
• Value cannot be null. (Parameter 'content')
• Must be > 1

AI-assisted analysis of spectreconsole/spectre.console@0acc92fada (2026-08-13). Data as JSON: /api/errors/793d1435b63049de. Report an issue: GitHub.