dotnet/wpf · error · ArgumentException

SR.Collection_NoNull

Error message

SR.Collection_NoNull

What it means

The FreezableCollection(T) constructor accepting an IEnumerable(T) throws ArgumentException (SR.Collection_NoNull) if any element of the source collection is null. Freezable collections never permit null items because null cannot be frozen/validated as a Freezable element.

Solutions

1. Filter nulls before constructing: collection.Where(x => x != null).
2. Fix the upstream producer so it never emits null elements.
3. If nulls are meaningful, wrap items in a nullable-holder type instead.

Example fix

// before
var col = new FreezableCollection<Geometry>(rawList);
// after
var col = new FreezableCollection<Geometry>(rawList.Where(g => g != null));

if (source.Any(item => item == null)) throw new InvalidOperationException("Source contains null items");

try { col = new FreezableCollection<T>(source); } catch (ArgumentException) { col = new FreezableCollection<T>(source.Where(x => x != null)); }

When it happens

Trigger: new FreezableCollection<T>(someEnumerable) where someEnumerable contains one or more null references.

Common situations: Initializing a collection from LINQ results, deserialized data, or an array built incrementally where nulls slipped in; e.g. new FreezableCollection<Geometry>(geometries) with geometries containing nulls.

Related errors

• DoubleKeyFrameCollection
• Int16KeyFrameCollection
• MatrixKeyFrameCollection
• ObjectKeyFrameCollection
• Point3DKeyFrameCollection

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/c9a8f79dc0d260b7. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/FreezableCollection.cs:81

            ArgumentNullException.ThrowIfNull(collection);

            int count = GetCount(collection);

            if (count > 0)
            {
                _collection = new List<T>(count);
            }
            else
            {
                _collection = new List<T>();
            }

            foreach (T item in collection)
            {
                if (item == null)
                {
                    throw new System.ArgumentException(SR.Collection_NoNull);
                }

                OnFreezablePropertyChanged(oldValue: null, item);

                _collection.Add(item);
            }

            WritePostscript();
        }

        #endregion Constructors

        //------------------------------------------------------
        //
        //  Public Methods
        //
        //------------------------------------------------------

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