What causes "GUID cannot be empty." in dotnet/wpf?

Supply a valid, non-empty Guid (e.g. a known ApplicationGuid or a newly generated Guid.NewGuid()) when adding the property.

dotnet/wpf · error · ArgumentException

GUID cannot be empty.

Error message

GUID cannot be empty.

What it means

The internal ExtendedProperty constructor requires a non-empty Guid identifying the ink attribute; Guid.Empty is rejected with ArgumentException(SR.InvalidGuid, 'GUID cannot be empty.'). Extended properties are keyed by GUID, so an empty id would create an unaddressable entry.

Solutions

Supply a valid, non-empty Guid (e.g. a known ApplicationGuid or a newly generated Guid.NewGuid()) when adding the property.
Check `id == Guid.Empty` before calling Add and skip or substitute a real id.
Fix upstream data so the GUID is preserved through serialization/deserialization.
If the guid was meant to be generated, replace default(Guid)/new Guid() placeholders with Guid.NewGuid().

Example fix

// before
properties.Add(Guid.Empty, value); // ArgumentException: GUID cannot be empty.
// after
Guid id = knownAttributeId != Guid.Empty ? knownAttributeId : Guid.NewGuid();
properties.Add(id, value);

Defensive patterns

Strategy: validation

Validate before calling

if (id == Guid.Empty)
    throw new ArgumentException("A valid non-empty GUID is required.", nameof(id));
properties.Add(id, value);

Type guard

static bool IsValidPropertyId(Guid id) => id != Guid.Empty;

Try / catch

try { properties.Add(id, value); }
catch (ArgumentException) { /* Guid.Empty id: fix the source of the guid */ }

Prevention

Never use default(Guid) as a placeholder
Validate guids at data-deserialization boundaries
Generate ids with Guid.NewGuid() when none exists

When it happens

Trigger: Constructing ExtendedProperty(Guid.Empty, value), or calling ExtendedPropertyCollection.Add(Guid.Empty, value), which forwards to this constructor.

Common situations: Loading ISF/ink data where a property GUID was lost or zeroed; deserializing hand-built ink XML with placeholder GUIDs; using default(Guid) as a placeholder before assigning a real attribute id.

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 dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/5602567b955cc601. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/Ink/ExtendedProperty.cs:23

namespace System.Windows.Ink
{
    /// <summary>
    /// Drawing Attribute Key/Value pair for specifying each attribute
    /// </summary>
    internal sealed class ExtendedProperty
    {
        /// <summary>
        /// Create a new drawing attribute with the specified key and value
        /// </summary>
        /// <param name="id">Identifier of attribute</param>
        /// <param name="value">Attribute value - not that the Type for value is tied to the id</param>
        /// <exception cref="System.ArgumentException">Value type must be compatible with attribute Id</exception>
        internal ExtendedProperty(Guid id, object value)
        {
            if (id == Guid.Empty)
            {
                throw new ArgumentException(SR.InvalidGuid);
            }
            _id = id;
            Value = value;
        }

        /// <summary>Returns a value that can be used to store and lookup
        /// ExtendedProperty objects in a hash table</summary>
        public override int GetHashCode()
        {
            return Id.GetHashCode() ^ Value.GetHashCode();
        }

        /// <summary>Determine if two ExtendedProperty objects are equal</summary>
        public override bool Equals(object obj)
        {
            if (obj == null || obj.GetType() != GetType())
            {
                return false;

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