dotnet/BenchmarkDotNet · error · ArgumentException

Property values can not contain null.

Error message

Property values can not contain null.

What it means

Thrown by CreateArgumentTextRepresentation when building an MSBuild-style /p:{name}={value} argument string and one of the provided string values in the array is null. This is a defensive precondition check: the method already guards against a null array and an empty name, then iterates each element to ensure none is null before joining them with ';'. A null element would otherwise silently produce a malformed argument like /p:Prop=a;foo; where a segment is missing.

Source

Thrown at src/BenchmarkDotNet/Jobs/Argument.cs:130

    [PublicAPI]
    public class MsBuildProperty : MsBuildArgument
    {
        public MsBuildProperty(string name, params string[] values)
            : base(CreateArgumentTextRepresentation(name, values), escapeSpecialCharacters: true)
        {
        }

        private static string CreateArgumentTextRepresentation(string name, string[] values)
        {
            if (string.IsNullOrWhiteSpace(name))
                throw new ArgumentException("Property name must be non-empty.", nameof(name));

            if (values is null)
                throw new ArgumentNullException(nameof(values));

            for (int i = 0; i < values.Length; i++)
                if (values[i] is null)
                    throw new ArgumentException("Property values can not contain null.", nameof(values));

            string value = values.Length switch
            {
                0 => string.Empty,
                1 => values[0],
                _ => string.Join(";", values)
            };

            return $"/p:{name}={value}";
        }
    }
}

View on GitHub (pinned to b515068b61)

Solutions

1. Filter out null entries before passing the array: values = values.Where(v => v != null).ToArray()
2. Ensure every element is assigned a non-null string when constructing the values array programmatically.
3. If nulls are semantically meaningful, decide on a sentinel (empty string) and coalesce: values.Select(v => v ?? string.Empty).ToArray()

Example fix

// before
var values = new string[] { "a", null, "b" };
var arg = Argument.CreateArgumentTextRepresentation("Prop", values);

// after
var values = new string[] { "a", null, "b" }
    .Where(v => v != null)
    .ToArray();
var arg = Argument.CreateArgumentTextRepresentation("Prop", values);

string[] values = /* ... */;
if (values != null && values.Any(v => v is null))
    values = values.Where(v => v != null).ToArray();
// safe to pass now

static bool HasNoNulls(string[] values) => values != null && values.All(v => v is not null);

When it happens

Trigger: Calling an API that internally constructs Argument text (e.g. Job/Characteristic settings that map to MSBuild properties) and passing a string[] that contains a null element. The loop `for (int i = 0; i < values.Length; i++) if (values[i] is null)` triggers the ArgumentException with paramName 'values'.

Common situations: Building a Job with array-valued properties (like environment variables or multi-value MSBuild properties) where one slot was never assigned, default-initialized to null, or came from a LINQ Select that returned null for a missing entry. Often seen when dynamically assembling argument lists from configuration dictionaries where some keys lack values.

Related errors

• Value cannot be null. (Parameter 'key')
• Value cannot be null. (Parameter 'value')
• The '{variable.Key}' environment variables is defined twice

AI-assisted analysis of dotnet/BenchmarkDotNet@b515068b61 (2026-08-13). Data as JSON: /api/errors/238095231ed0c3de. Report an issue: GitHub.