JwtBearerHandler.HandleAuthenticateAsync() - Object reference not set to an instance of an object.

[RedBlack-DevOps]

We were getting the below error in one of our projects.

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.AspNetCore.Authentication.JwtBearer.JwtBearerHandler.HandleAuthenticateAsync()
   at Microsoft.AspNetCore.Authentication.JwtBearer.JwtBearerHandler.HandleAuthenticateAsync()
   at Microsoft.AspNetCore.Authentication.AuthenticationHandler`1.AuthenticateAsync()
   at Microsoft.AspNetCore.Authentication.AuthenticationService.AuthenticateAsync(HttpContext context, String scheme)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Server.IIS.Core.IISHttpContextOfT`1.ProcessRequestAsync()

We resolved it by changing the example LegacyOAuthSecurityTokenHandler to return validatedToken = new DummyWebToken();instead of validatedToken = default(SecurityToken);

public class DummyWebToken : SecurityToken
{
    public override string Id => "Id";

    public override string Issuer => "Issuer";

    public override DateTime ValidFrom => new DateTime();

    public override DateTime ValidTo => new DateTime();

    public override SecurityKey SecurityKey => throw new NotImplementedException();

    public override SecurityKey SigningKey { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
}