dotnet/wpf · error · ArgumentNullException

input or compressed data was null in Compress

Error message

input or compressed data was null in Compress

What it means

GorillaCodec.Compress validates its inputs: the int[] payload (input) and the List<byte> output (compressedData) must both be non-null, otherwise ArgumentNullException is thrown with this message. Gorilla compression is used internally when serializing stroke packet data to ISF; passing null buffers is a programming error by the caller.

Solutions

1. Allocate the output buffer before compressing: compressedData = new List<byte>();
2. Ensure input packet array is created and populated (even empty) rather than null.
3. Add null checks/guards in the calling code before invoking Compress.
4. Prefer the public StrokeCollection.Save API which initializes all buffers for you.

Example fix

// before
List<byte> compressedData = null;
codec.Compress(8, packetData, 0, dtxf, compressedData);
// after
List<byte> compressedData = new List<byte>(packetData.Length);
codec.Compress(8, packetData, 0, dtxf, compressedData);

if (input == null) throw new ArgumentNullException(nameof(input));
if (compressedData == null) throw new ArgumentNullException(nameof(compressedData));

bool CanCompress(int[] input, List<byte> outBuf) => input != null && outBuf != null;

try { codec.Compress(bitCount, packets, 0, dtxf, outBuf); }
catch (ArgumentNullException ex) { log.Error("Gorilla compress buffers missing", ex); throw; }

When it happens

Trigger: Calling Compress(bitCount, input, startInputIndex, dtxf, compressedData) with input == null or compressedData == null — typically in custom code that drives the Gorilla codec directly or a bug in a custom data pipeline that forgot to allocate the output list.

Common situations: Custom ink serialization code reusing GorillaCodec; refactoring that left a list uninitialized before compression; unit tests exercising the codec with placeholder nulls.

Related errors

• reader or compressedData was null in compress
• bogus GorillaEncodingType passed to compress
• Transform returned unexpected results
• bogus GorillaEncodingType passed to GetDataFromReader
• bogus GorillaEncodingType passed to Uncompress

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/3243e7bd05848c17. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/Ink/InkSerializedFormat/GorillaCodec.cs:362

            {
                bitCount = (int)_gorIndexMap[index].BitCount;
                padCount = (int)_gorIndexMap[index].PadCount;
            }
        }

        /// <summary>
        /// Compress - compress the input[] into compressedData
        /// </summary>
        /// <param name="bitCount">The count of bits needed for all elements</param>
        /// <param name="input">input buffer</param>
        /// <param name="startInputIndex">offset into the input buffer</param>
        /// <param name="dtxf">data transform.  can be null</param>
        /// <param name="compressedData">The list of bytes to write the compressed input to</param>
        internal void Compress(int bitCount, int[] input, int startInputIndex, DeltaDelta dtxf, List<byte> compressedData)
        {
            if (null == input || null == compressedData)
            {
                throw new ArgumentNullException(StrokeCollectionSerializer.ISFDebugMessage("input or compressed data was null in Compress"));
            }
            ArgumentOutOfRangeException.ThrowIfNegative(bitCount);

            if (bitCount == 0)
            {
                //adjust if the bitcount is 0
                //(this makes bitCount 32)
                bitCount = (int)(Native.SizeOfInt << 3);
            }

            //have the writer adapt to the List<byte> passed in and write to it
            BitStreamWriter writer = new BitStreamWriter(compressedData);
            if (null != dtxf)
            {
                int xfData = 0;
                int xfExtra = 0;
                for (int i = startInputIndex; i < input.Length; i++)
                {

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