static types cannot be used as type arguments

I am porting from traditional .net mvc application to .netcore.

I have a static class for reading connectionstring from appsettings.

public static class WPSGlobalSettings{    public static NpgsqlConnectionStringBuilder ToolboxConnString = build_conn_str(ToolboxDatabaseName);private static NpgsqlConnectionStringBuilder build_conn_str(string dbname)    {        string dbSetting = ConfigurationHelper.config.GetSection("ConnectionStrings")["DefaultConnection"];    ...    }}

Controller

public class StatusController : Microsoft.AspNetCore.Mvc.ControllerBase{    protected StatusDAL status_dal = new StatusDAL(WPSGlobalSettings.ToolboxConnString);}

Here it gives type exception, wpsglobalsettings was not initialized and toolboxconnstring is null.

I have tried adding it as singleton to Startup but then i get

static types cannot be used as type arguments

Startup.cs

public void ConfigureServices(IServiceCollection services){     services.AddSingleton<IConfiguration>(Configuration);        services.AddControllersWithViews();    services.AddSingleton<WPSGlobalSettings>();        ConfigurationHelper.Initialize(Configuration);}public void Configure(IApplicationBuilder app, IWebHostEnvironment env){        if (env.IsDevelopment())        {            app.UseDeveloperExceptionPage();        }        WPSGlobalSettings.Configure(env); ...}

A similar application seems to work fine the same way.

Edit:

I have removed following from Startup.cs

 services.AddSingleton<WPSGlobalSettings>();

Also, introduced DI as follows

protected StatusDAL status_dal;//= new StatusDAL(WPSGlobalSettings.ToolboxConnString);public StatusController(IConfiguration config)    {            status_dal = new StatusDAL(config.GetConnectionString("toolboxConnectionStrWPS"));    }

Now the problem is older code calls controller constructor from another class as follows:

OSMDB_Loader.cs

public StatusAck LoadOSMSections(OsmLoadRequest request)    {        StatusAck statusack = new StatusController().PostStatusRecord();     }

Therefore I also added simple constructor in StatusController:

public StatusController()    {    }

but now ofcourse status_dal is always null

Something is not quiet right!