dotnet/aspnetcore · error · ArgumentException

The parameter ' ' for component ' ' does not allow null or…

Error message

The parameter '{nameof(Name)}' for component '{nameof(CascadingValue<TValue>)}' does not allow null or empty values.

What it means

Thrown by CascadingValue when the Name parameter is supplied with null or an empty string. A non-empty Name is required when supplying a named cascading value so that consumers can match it via a [CascadingParameter(Name = ...)]. The check runs during parameter setting, surfacing the misuse immediately.

Solutions

1. Provide a non-empty, stable Name on the CascadingValue component (e.g. Name="theme").
2. If the value is anonymous/unnamed, omit the Name attribute entirely (unnamed cascade).
3. If Name is data-driven, guard the markup so <CascadingValue Name=...> only renders when the name is non-empty.

Example fix

<!-- before: empty name -->
<CascadingValue Name="" Value="dark">
    <ThemedComponent />
</CascadingValue>

<!-- after: real name -->
<CascadingValue Name="theme" Value="dark">
    <ThemedComponent />
</CascadingValue>

if (string.IsNullOrEmpty(name)) { throw new ArgumentException("CascadingValue.Name must be non-empty.", nameof(name)); }

static bool IsValidCascadingName(string? name) => !string.IsNullOrEmpty(name);

When it happens

Trigger: Authoring <CascadingValue Name=""> or passing a runtime value that resolves to null/empty for the Name parameter, while still attempting to provide a named cascade.

Common situations: Binding Name to a model property that is sometimes null; refactoring that leaves Name=""; copy-paste from a tutorial where the name was a placeholder.

Related errors

• ' ' is flagged with SingleDelivery, but the selected…
• Authorization requires a cascading parameter of type Task
• Do not specify both 'Authorized' and 'ChildContent'.
• The authorization data specifies an authentication scheme…
• The type ' ' does not have an associated TypeConverter that…

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/d17c1af4f5e980d1. Report an issue: GitHub.

Appendix: source

Thrown at src/Components/Components/src/CascadingValue.cs:81

        IsFixed = false;

        foreach (var parameter in parameters)
        {
            if (parameter.Name.Equals(nameof(Value), StringComparison.OrdinalIgnoreCase))
            {
                Value = (TValue)parameter.Value;
                hasSuppliedValue = true;
            }
            else if (parameter.Name.Equals(nameof(ChildContent), StringComparison.OrdinalIgnoreCase))
            {
                ChildContent = (RenderFragment)parameter.Value;
            }
            else if (parameter.Name.Equals(nameof(Name), StringComparison.OrdinalIgnoreCase))
            {
                Name = (string)parameter.Value;
                if (string.IsNullOrEmpty(Name))
                {
                    throw new ArgumentException($"The parameter '{nameof(Name)}' for component '{nameof(CascadingValue<TValue>)}' does not allow null or empty values.");
                }
            }
            else if (parameter.Name.Equals(nameof(IsFixed), StringComparison.OrdinalIgnoreCase))
            {
                IsFixed = (bool)parameter.Value;
            }
            else
            {
                throw new ArgumentException($"The component '{nameof(CascadingValue<TValue>)}' does not accept a parameter with the name '{parameter.Name}'.");
            }
        }

        if (_hasSetParametersPreviously && IsFixed != previousFixed)
        {
            throw new InvalidOperationException($"The value of {nameof(IsFixed)} cannot be changed dynamically.");
        }

        _hasSetParametersPreviously = true;

View on GitHub (pinned to 3600ca084e)