microsoft/aspire · error · ArgumentException

Exporting assembly names cannot be null or white-space.

Error message

Exporting assembly names cannot be null or white-space.

What it means

ApiReferenceExportOptions validates that every entry in exportingAssemblyNames is a non-null, non-whitespace string and throws ArgumentException otherwise. It rejects partially-invalid collections rather than silently dropping bad entries.

Solutions

1. Remove null/blank entries from the collection before constructing options
2. If parsing a delimited string, split then filter with Where(n => !string.IsNullOrWhiteSpace(n))
3. Fix the source data (config/CLI input) that produced blank names

Example fix

// before
new ApiReferenceExportOptions(pkg, ver, raw.Split(','));
// after
new ApiReferenceExportOptions(pkg, ver, raw.Split(',').Where(n => !string.IsNullOrWhiteSpace(n)).ToArray());

var clean = raw.Where(n => !string.IsNullOrWhiteSpace(n)).ToArray();
if (clean.Length == 0) throw new ArgumentException("No valid assembly names.");

try { var o = new ApiReferenceExportOptions(pkg, ver, rawNames); }
catch (ArgumentException ex) { logger.LogError(ex, "Blank assembly name in export options"); }

When it happens

Trigger: Passing a collection containing null, empty, or whitespace-only assembly names to new ApiReferenceExportOptions.

Common situations: Assembly lists assembled by splitting a comma-separated string with empty items (e.g. "A,,B"), or nulls introduced by deserialization of sparse arrays.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• At least one exporting assembly name is required.
• Array params contains empty item
• Endpoint option ' ' is configured more than once.
• Endpoint option names cannot be empty.
• Endpoint options cannot contain null values.

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/894f9f0b2f4c430e. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.TypeSystem/ApiReferenceExportOptions.cs:56

    /// Thrown when <paramref name="packageName"/> or <paramref name="packageVersion"/> is empty or
    /// consists only of white-space characters, or when <paramref name="exportingAssemblyNames"/>
    /// is empty or contains a null, empty, or white-space assembly name.
    /// </exception>
    public ApiReferenceExportOptions(
        string packageName,
        string packageVersion,
        IReadOnlyCollection<string> exportingAssemblyNames)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(packageName);
        ArgumentException.ThrowIfNullOrWhiteSpace(packageVersion);
        ArgumentNullException.ThrowIfNull(exportingAssemblyNames);
        if (exportingAssemblyNames.Count == 0)
        {
            throw new ArgumentException("At least one exporting assembly name is required.", nameof(exportingAssemblyNames));
        }
        if (exportingAssemblyNames.Any(string.IsNullOrWhiteSpace))
        {
            throw new ArgumentException("Exporting assembly names cannot be null or white-space.", nameof(exportingAssemblyNames));
        }

        PackageName = packageName;
        PackageVersion = packageVersion;
        ExportingAssemblyNames = Array.AsReadOnly(exportingAssemblyNames.ToArray());
    }

    /// <summary>
    /// Gets the name of the package being exported.
    /// </summary>
    public string PackageName { get; }

    /// <summary>
    /// Gets the version label recorded for this export, as supplied by the caller.
    /// </summary>
    /// <remarks>
    /// Consumers key published documentation on this value, so callers are expected to pass the
    /// exact version that was restored. Nothing on this type can confirm that: an exporter sees

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