dotnet/wpf · error · ArgumentNullException

DecimalKeyFrameCollection

Error message

DecimalKeyFrameCollection[{0}]

What it means

DecimalKeyFrameCollection's public indexer setter throws ArgumentNullException when null is assigned, with the parameter name "DecimalKeyFrameCollection[{index}]" identifying the slot. Every element must be a non-null DecimalKeyFrame.

Solutions

  1. Assign a valid DecimalKeyFrame instance instead of null
  2. Use RemoveAt(index) to remove the slot
  3. Null-check the key frame before assigning
  4. Repair the data source so it never supplies null key frames

Example fix

// before
keyFrames[2] = null; // ArgumentNullException
// after
if (frame != null) keyFrames[2] = frame; else keyFrames.RemoveAt(2);
Defensive patterns

Strategy: type-guard

Validate before calling

if (frame == null) keyFrames.RemoveAt(index); else keyFrames[index] = frame;

Type guard

static bool IsValidDecimalKeyFrame(DecimalKeyFrame frame) => frame != null;

Try / catch

try { keyFrames[i] = frame; }
catch (ArgumentNullException ex) when (ex.ParamName == $"DecimalKeyFrameCollection[{i}]") { /* remove the slot or substitute a default frame */ }

Prevention

When it happens

Trigger: Executing decimalKeyFrames[i] = null, or downstream paths that assign a null key frame into an existing index of the collection.

Common situations: Data-bound sources producing null items; clear-by-assignment patterns; deserialization gaps yielding null entries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/09060a0585304e42. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/Generated/DecimalKeyFrameCollection.cs:466

            }
        }

        /// <summary>
        /// Gets or sets the DecimalKeyFrame at a given index.
        /// </summary>
        public DecimalKeyFrame this[int index]
        {
            get
            {
                ReadPreamble();

                return _keyFrames[index];
            }
            set
            {
                if (value == null)
                {
                    throw new ArgumentNullException(String.Format(CultureInfo.InvariantCulture, "DecimalKeyFrameCollection[{0}]", index));
                }

                WritePreamble();

                if (value != _keyFrames[index])
                {
                    OnFreezablePropertyChanged(_keyFrames[index], value);
                    _keyFrames[index] = value;

                    Debug.Assert(_keyFrames[index] != null);

                    WritePostscript();
                }
            }
        }

        #endregion
    }

View on GitHub (pinned to 81131a70a4)