dotnet/yarp · error · ArgumentException

'key' cannot be null or empty.

Error message

'key' cannot be null or empty.

What it means

Thrown by the QueryParameterRemoveTransform constructor when `key` is null or empty. The transform removes a named query parameter; without a name there is nothing to remove, so it is rejected as ArgumentException on `key`.

Source

Thrown at src/ReverseProxy/Transforms/QueryParameterRemoveTransform.cs:18

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Threading.Tasks;

namespace Yarp.ReverseProxy.Transforms;

/// <summary>
/// A request transform that removes the given query parameter.
/// </summary>
public class QueryParameterRemoveTransform : RequestTransform
{
    public QueryParameterRemoveTransform(string key)
    {
        if (string.IsNullOrEmpty(key))
        {
            throw new ArgumentException($"'{nameof(key)}' cannot be null or empty.", nameof(key));
        }

        Key = key;
    }

    internal string Key { get; }

    /// <inheritdoc/>
    public override ValueTask ApplyAsync(RequestTransformContext context)
    {
        ArgumentNullException.ThrowIfNull(context);

        context.Query.Collection.Remove(Key);

        return default;
    }
}

View on GitHub (pinned to bd11867bee)

Solutions

1. Provide a non-empty query-parameter name to remove.
2. Validate the key before constructing if sourced from input.
3. Fix the transform config to include the key.

Example fix

// before
new QueryParameterRemoveTransform("");
// after
new QueryParameterRemoveTransform("tracking");

ArgumentException.ThrowIfNullOrEmpty(key);

static bool IsValidQueryKey(string? key) => !string.IsNullOrEmpty(key);

When it happens

Trigger: Constructing `new QueryParameterRemoveTransform(key)` with `key` null/empty/whitespace, or via transform config that omits the query parameter name to remove.

Common situations: Config sets a query-remove transform with no key. Programmatic construction from input that yielded an empty key.

Related errors

• '{nameof(key)}' cannot be null or empty.
• '{nameof(routeValueKey)}' cannot be null or empty.
• '{nameof(key)}' cannot be null or empty.
• 'key' cannot be null or empty.
• '{nameof(fromMethod)}' cannot be null or empty.

AI-assisted analysis of dotnet/yarp@bd11867bee (2026-08-13). Data as JSON: /api/errors/355fead469272056. Report an issue: GitHub.