What causes "Anchor value must not be empty." in stride3d/stride?

Pass null instead of "" when a node has no anchor

stride3d/stride · error · ArgumentException

Anchor value must not be empty.

Error message

Anchor value must not be empty.

What it means

NodeEvent is the base class of scalar/sequence/mapping events; when an anchor is supplied it must be non-empty. Unlike the alias variant, this check throws System.ArgumentException (not YamlException) because it is a constructor argument validation on the event object itself.

Solutions

Pass null instead of "" when a node has no anchor
Coerce empty strings to null before constructing the event
Validate anchor names before building node events
Fix producers that initialize anchor fields to empty strings

Example fix

// before
var evt = new Scalar(anchor ?? "", tag, value, style, true, false, start, end);
// after
var evt = new Scalar(string.IsNullOrEmpty(anchor) ? null : anchor, tag, value, style, true, false, start, end);

Defensive patterns

Strategy: validation

Validate before calling

string safeAnchor = string.IsNullOrEmpty(anchor) ? null : anchor;
if (safeAnchor != null && !safeAnchor.All(char.IsLetterOrDigit)) throw new ArgumentException("Invalid anchor");

Try / catch

try { var evt = new Scalar(anchor, tag, value, style, true, false, start, end); }
catch (ArgumentException ex) when (ex.ParamName == "anchor") { /* coerce to null and rebuild */ }

Prevention

Use null, not string.Empty, for 'no anchor'
Catch ArgumentException (not YamlException) around node event constructors
Normalize anchor fields at the source so they are either null or valid

When it happens

Trigger: Passing anchor: "" (not null) to a ScalarEvent/SequenceStartEvent/MappingStartEvent constructor, e.g. new Scalar("", tag, value, ...) — null means 'no anchor', empty string is invalid.

Common situations: Serialization code that defaults anchors with string.Empty instead of null; template interpolation producing ""; converters that emit an anchor attribute for every node even when empty.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/83814be16622b5d8. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Events/NodeEvent.cs:94

        /// </summary>
        /// <value></value>
        public abstract bool IsCanonical { get; }

        /// <summary>
        /// Initializes a new instance of the <see cref="NodeEvent"/> class.
        /// </summary>
        /// <param name="anchor">The anchor.</param>
        /// <param name="tag">The tag.</param>
        /// <param name="start">The start position of the event.</param>
        /// <param name="end">The end position of the event.</param>
        protected NodeEvent(string anchor, string tag, Mark start, Mark end)
            : base(start, end)
        {
            if (anchor != null)
            {
                if (anchor.Length == 0)
                {
                    throw new ArgumentException("Anchor value must not be empty.", "anchor");
                }

                if (!anchorValidator.IsMatch(anchor))
                {
                    throw new ArgumentException("Anchor value must contain alphanumerical characters only.", "anchor");
                }
            }

            if (tag != null && tag.Length == 0)
            {
                throw new ArgumentException("Tag value must not be empty.", "tag");
            }

            this.anchor = anchor;
            this.tag = tag;
        }

        /// <summary>

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