Constructor dependencies injection

I'm creating a new service via an interface and I'm not skilled enough to get this right. While implementing the code I've got an issue I can't overcome: _infoSAP is getting null value because it is not instiantiated correctly and I can't find how to do it properly. See code below, issue occurs at CreateCustomerSAP line.

// all 'using' needed
namespace OurBrand.Controllers
{
    public class AccountController : RootController
    {   
        private readonly IModuleSAP _infoSAP;

        //CodeLens: 0 references
        public AccountController()
        {
        }

        //CodeLens: 1 references    
        public AccountController(IModuleSAP customerSAP)
        {
            _infoSAP = customerSAP;
        }

        //CodeLens: 0 references
        public AccountController(IUserData userData, IMapper mapper, ICheckCompanyNumber checkCompanyNumber)
        {
            _userData = userData;
            _mapper = mapper;
            _checkCompanyNumber = checkCompanyNumber;
        }

        public JsonResult APITest(string testValue)
        {    
            var newCustomerSAP = new CustomerSAP_DTO()
            {
                //Properties
            };

            // Here the error occurs: "_infoSAP" is null
            _infoSAP.CreateCustomerSAP(customerDataSAP);

            return Json(new
            {
                success = true,
            }, JsonRequestBehavior.AllowGet);
        }
    }
}

Interface:

namespace OurBrand.External.Services.Interfaces
{
    public interface IModuleSAP
    {
        void CreateCustomerSAP(CustomerSAP_DTO customerData);
    }
}

Service:

// all 'using' needed
namespace OurBrand.External.Services
{
    public class ModuleSAP : IModuleSAP
    {
        public void CreateCustomerSAP(CustomerSAP_DTO customerData)
        {
            // Code here

            return;
        }
    }
}

The fact that you have 3 constructors with completely different arguments is a big red flag. the point of a constructor is to ensure that an object is initialized with everything it will need to execute the methods and such it exposes. Constructors that expose different properties for different scenarios should be avoided because there is no guarantee, especially with dependency injection containers that the correct constructor would have been used for the instance for the method you are calling.

Codelens results are useless for constructor usage with IoC containers because there is no code to inspect for where the constructor would be called. The container will use reflection to discover and instantiate a class instance so they should all report 0 usages. The fact that you have 1 usage for a constructor means you have code that is breaking DI and new-ing up a reference of that class somewhere.

So your class should ideally have one constructor:

    public AccountController(IUserData userData, IMapper mapper, ICheckCompanyNumber checkCompanyNumber, IModuleSAP customerSAP)
    {
        _userData = userData;
        _mapper = mapper;
        _checkCompanyNumber = checkCompanyNumber;
        _infoSAP = customerSAP;
    }

The issue you are likely encountering is that the instance of the account controller being resolved by the container was actually picking the other constructor leaving your _infoSAP reference uninitialized.

I've found that my issue was at RegisterTypes, the newly created IModuleSAP was not there. After its creation, things became operative again.

While it was important to notice Steve Py message, only with a support of another DEV that I could find the missing point stated above.