What causes "nameof(values)" in dotnet/machinelearning?

Coalesce to empty: values ?? Enumerable.Empty ().

dotnet/machinelearning · error · ArgumentNullException

nameof(values)

Error message

nameof(values)

What it means

PrimitiveColumnContainer<T>(IEnumerable<T> values) rejects a null enumerable with ArgumentNullException(nameof(values)); it then appends each value. This is a fail-fast guard — the elements themselves may be any T.

Source

Thrown at src/Microsoft.Data.Analysis/PrimitiveColumnContainer.cs:30

namespace Microsoft.Data.Analysis
{
    /// <summary>
    /// PrimitiveColumnContainer is just a store for the column data. APIs that want to change the data must be defined in PrimitiveDataFrameColumn
    /// </summary>
    /// <typeparam name="T"></typeparam>
    internal partial class PrimitiveColumnContainer<T> : IEnumerable<T?>
        where T : unmanaged
    {
        public IList<ReadOnlyDataFrameBuffer<T>> Buffers = new List<ReadOnlyDataFrameBuffer<T>>();

        // To keep the mapping simple, each buffer is mapped 1v1 to a nullBitMapBuffer
        // A set bit implies a valid value. An unset bit => null value
        public IList<ReadOnlyDataFrameBuffer<byte>> NullBitMapBuffers = new List<ReadOnlyDataFrameBuffer<byte>>();

        public PrimitiveColumnContainer(IEnumerable<T> values)
        {
            values = values ?? throw new ArgumentNullException(nameof(values));
            foreach (T value in values)
            {
                Append(value);
            }
        }

        public PrimitiveColumnContainer(IEnumerable<T?> values)
        {
            values = values ?? throw new ArgumentNullException(nameof(values));
            foreach (T? value in values)
            {
                Append(value);
            }
        }

        public PrimitiveColumnContainer(ReadOnlyMemory<byte> buffer, ReadOnlyMemory<byte> nullBitMap, int length, int nullCount)
        {
            ReadOnlyDataFrameBuffer<T> dataBuffer;

View on GitHub (pinned to 7b76e69cf9)

Solutions

Coalesce to empty: values ?? Enumerable.Empty<T>().
Null-check at the call site before constructing.
Fix the producer method to return an empty sequence rather than null.
Initialize collections with Array.Empty<T>() instead of null.

Example fix

// before
var container = new PrimitiveColumnContainer<int>(GetValues()); // may return null
// after
var values = GetValues() ?? Enumerable.Empty<int>();
var container = new PrimitiveColumnContainer<int>(values);

Defensive patterns

Strategy: validation

Validate before calling

if (values is null)
    throw new ArgumentException("values must not be null; pass an empty sequence instead");

Type guard

bool isUsableSequence<T>(IEnumerable<T> values) => values is not null;

Try / catch

try { var c = new PrimitiveColumnContainer<int>(values); }
catch (ArgumentNullException ex) when (ex.ParamName == "values")
{ /* null enumerable: coalesce to Enumerable.Empty<int>() and retry */ }

Prevention

Coalesce possibly-null sequences with ?? Enumerable.Empty<T>().
Return empty collections, never null, from producers.
Enable nullable reference types to catch null flows at compile time.
Default-initialize collections to Array.Empty<T>().

When it happens

Trigger: Passing a null IEnumerable<T> to the constructor, typically from an uninitialized variable or a method returning null instead of an empty sequence.

Common situations: Deserialized configuration holding null collections; helper methods returning null on failure; dictionary lookups yielding null lists.

Related errors

AI-assisted analysis of dotnet/machinelearning@7b76e69cf9 (2026-09-11). Data as JSON: /api/errors/b2f90755670737bc. Report an issue: GitHub.