Properties should not return arrays (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1819)

Rename type name ResponseHandlerDelegate so that it does not end in 'Delegate' (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1711)

'task is null' is always 'true'. Remove or refactor the condition(s) to avoid dead code. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1508)

Random is an insecure random number generator. Use cryptographically secure random number generators when randomness is required for security. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca5394)

Exception type System.IndexOutOfRangeException is reserved by the runtime (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2201)

Random is an insecure random number generator. Use cryptographically secure random number generators when randomness is required for security. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca5394)

Consider calling ConfigureAwait on the awaited task (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2007)

In virtual/interface member IResponseBehavior.HandleAsync(MockHttpRequestContext, HttpResponseMessage, ResponseHandlerDelegate, CancellationToken), rename parameter next so that it no longer conflicts with the reserved language keyword 'Next'. Using a reserved keyword as the name of a parameter on a virtual/interface member makes it harder for consumers in other languages to override/implement the member. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1716)

Modify 'TryAdd' to catch a more specific allowed exception type, or rethrow the exception (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1031)

Call the ArgumentOutOfRangeException constructor that contains a message and/or paramName parameter (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2208)

The target framework 'net5.0' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'netcoreapp2.1' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'net5.0' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'netcoreapp2.1' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'net5.0' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'netcoreapp2.1' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'net5.0' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'netcoreapp2.1' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'net5.0' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.