I want to read the connection string defined in host.json in my Startup class.The problem is when running IConfiguration is always null !

using Microsoft.Azure.Functions.Extensions.DependencyInjection;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Configuration;

[assembly: FunctionsStartup(typeof(MyNamespace.Startup))]

namespace MyNamespace
{
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            var configuration = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("host.json", optional: true, reloadOnChange: true)
                .AddEnvironmentVariables().Build();

            IConfiguration conf = configuration;

            builder.Services.AddSingleton(conf);
            builder.Services.AddHttpClient();
        }
    }
}

This is the Startup Class i defined for my dependency injection of the IConfiguration !

using FirstFunction.dto;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
using System.Globalization;
using System.Text;
using Azure.Storage.Queues;
using Azure.Storage.Queues.Models;
using Microsoft.Extensions.Configuration;
using System.Reflection;

namespace FirstFunction
{
    public class Function1
    {
        private readonly ILogger<Function1> _logger;
        private readonly IConfiguration _configuration;
        private readonly HttpClient _httpClient;

        public Function1(ILogger<Function1> logger)
        {
            _logger = logger;
        }

        public Function1(ILogger<Function1> logger, IConfiguration configuration, HttpClient httpClient) : this(logger)
        {
            _configuration = configuration;
            _httpClient = httpClient;
        }

        [Function("Function1")]
        public async Task<IActionResult> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequest req)
        {
            #region Catch Error
            string requestBody = string.Empty;
            try
            {
                requestBody = await new StreamReader(req.Body).ReadToEndAsync();
            }
            catch (Exception ex)
            {
                _logger.LogError($"Error reading request body: {ex.Message}");
                return new StatusCodeResult(StatusCodes.Status500InternalServerError);
            }
            #endregion

            string myConnectionString = _configuration["ConnectionStrings:QUEUE_CONNECTION_STRING"];

 return new  OkObjectResult("Data was sent to backend");
        }
    }
}

This is my azure Function method. The code is shortened

using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

var host = new HostBuilder()
    .ConfigureFunctionsWebApplication()
    .ConfigureServices(services =>
    {
        services.AddApplicationInsightsTelemetryWorkerService();
        services.ConfigureFunctionsApplicationInsights();
    })
    .Build();

host.Run();

This was generated called Programm.cs

The error message is not so exact because of that i let it slide!

thank you for your help !