What causes "SR.Collection_NoNull" in dotnet/wpf?

Guard with a null check before inserting and skip null segments.

dotnet/wpf · error · ArgumentException

SR.Collection_NoNull

Error message

SR.Collection_NoNull

What it means

PathSegmentCollection.Insert throws ArgumentException with SR.Collection_NoNull when a null PathSegment is inserted. Null items are disallowed because segments participate in Freezable change notification and geometry rendering.

Solutions

Guard with a null check before inserting and skip null segments.
Substitute a benign default segment (e.g. LineSegment) when the value would be null.
Fix the upstream factory/parsing code that produced a null segment.

Example fix

// before
segments.Insert(0, maybeSegment);
// after
if (maybeSegment != null)
{
    segments.Insert(0, maybeSegment);
}

Defensive patterns

Strategy: validation

Validate before calling

if (segment == null) return; // or throw with context
segments.Insert(index, segment);

Type guard

bool IsValidSegment(PathSegment s) => s != null;

Prevention

Null-check segment factory results before insertion.
Use a default segment type (LineSegment) rather than null placeholders.

When it happens

Trigger: Calling PathSegmentCollection.Insert(index, null) or IList.Insert with a null value; collection-initializer expressions that add a null segment.

Common situations: Building path geometry from optional segments where a line/arc variable is null; results of a factory method that returned null on failure being inserted directly.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/e6f012add920fa93. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Generated/PathSegmentCollection.cs:128

        /// <summary>
        ///     Returns the index of "value" in the list
        /// </summary>
        public int IndexOf(PathSegment value)
        {
            ReadPreamble();

            return _collection.IndexOf(value);
        }

        /// <summary>
        ///     Inserts "value" into the list at the specified position
        /// </summary>
        public void Insert(int index, PathSegment value)
        {
            if (value == null)
            {
                throw new System.ArgumentException(SR.Collection_NoNull);
            }

            WritePreamble();

            OnFreezablePropertyChanged(/* oldValue = */ null, /* newValue = */ value);

            _collection.Insert(index, value);



            ++_version;
            WritePostscript();
        }

        /// <summary>
        ///     Removes "value" from the list
        /// </summary>
        public bool Remove(PathSegment value)

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