What causes "Cannot have empty query parameter names." in dotnet/aspnetcore?

Filter out null/empty keys before calling GetUriWithQueryParameters.

dotnet/aspnetcore · error · InvalidOperationException

Cannot have empty query parameter names.

Error message

Cannot have empty query parameter names.

What it means

The QueryParameterSource<TValue> constructor throws InvalidOperationException when the parameter name is null or empty. Query parameter names are required to build a valid querystring; an empty name would produce malformed output.

Source

Thrown at src/Components/Components/src/NavigationManagerExtensions.cs:166

            _builder.Append(hash);
        }
    }

    // A utility for feeding a collection of parameter values into a QueryStringBuilder.
    // This is used when generating a querystring with a query parameter that has multiple values.
    private readonly struct QueryParameterSource<TValue>
    {
        private readonly IEnumerator<TValue?>? _enumerator;
        private readonly QueryParameterFormatter<TValue>? _formatter;

        public string EncodedName { get; }

        // Creates an empty instance to simulate a source without any elements.
        public QueryParameterSource(string name)
        {
            if (string.IsNullOrEmpty(name))
            {
                throw new InvalidOperationException(EmptyQueryParameterNameExceptionMessage);
            }

            EncodedName = Uri.EscapeDataString(name);

            _enumerator = default;
            _formatter = default;
        }

        public QueryParameterSource(string name, IEnumerable<TValue?> values, QueryParameterFormatter<TValue> formatter)
            : this(name)
        {
            _enumerator = values.GetEnumerator();
            _formatter = formatter;
        }

        public bool TryAppendNextParameter(ref QueryStringBuilder builder)
        {
            if (_enumerator is null || !_enumerator.MoveNext())

View on GitHub (pinned to 294cab2f9b)

Solutions

Filter out null/empty keys before calling GetUriWithQueryParameters.
Validate parameter names are non-empty at the source (e.g. form binding).
Use strongly-typed overloads (GetUriWithQueryParameter<T>) which still require a name check.

Example fix

// before
var qs = navManager.GetUriWithQueryParameters(new Dictionary<string,object?> { [""] = 1 });

// after
var qs = navManager.GetUriWithQueryParameters(parameters.Where(p => !string.IsNullOrEmpty(p.Key)).ToDictionary());

Defensive patterns

Strategy: validation

Validate before calling

var filtered = parameters
    .Where(p => !string.IsNullOrEmpty(p.Key))
    .ToDictionary(p => p.Key, p => p.Value);
var uri = navManager.GetUriWithQueryParameters(filtered);

Type guard

static bool HasNoEmptyNames(IReadOnlyDictionary<string,object?> p) =>
    p.All(kv => !string.IsNullOrEmpty(kv.Key));

Try / catch

try { uri = navManager.GetUriWithQueryParameters(parameters); }
catch (InvalidOperationException ex) when (ex.Message.Contains("empty query parameter names"))
{ logger.LogWarning(ex, "Filtered out empty query names");
  uri = navManager.GetUriWithQueryParameters(parameters.Where(kv => !string.IsNullOrEmpty(kv.Key)).ToDictionary()); }

Prevention

Sanitize dynamic dictionaries before building query strings.
Use constants or nameof for parameter names.
Add a unit test asserting no empty keys reach the API.

When it happens

Trigger: Passing an empty string or null as the dictionary key/name to GetUriWithQueryParameters; a dictionary with a whitespace/empty key used for query construction; reflection-driven code producing empty parameter names.

Common situations: Building query parameters from dynamic data where a key is missing; deserializing a dictionary that includes empty keys; copy-paste leaving a placeholder empty key.

Related errors

AI-assisted analysis of dotnet/aspnetcore@294cab2f9b (2026-08-06). Data as JSON: /api/errors/2006d0c7b281956d. Report an issue: GitHub.