I have an endpoint:

http://localhost:5235/ProductsEF/GetSubstances/ApapExtra

where I get the result, for example /ApapExtra:

{
    "productId": 4,
    "productName": "ApapExtra",
    "substance1": "Paracetamolum",
    "substance2": "Coffeinum",
    "substance3": null,
    "substance4": null
}

And I have another endpoint:

http://localhost:5235/SubstancesEF/GetSubstanceDataByName/Paracetamolum

where I get the data like, for example /Paracetamolum:

{
    "substanceId": 4,
    "name": "Paracetamolum",
    "effect": "Analgesic"
}

I want to combine them in one method. I want to create a method:

[HttpGet("GetSubstances/{ProductName}")]
public Product GetSubstancesFromProduct(string ProductName)
{
    Product product = _productRepository.GetProductDataByName(ProductName);

    if (product == null)
    {
        throw new Exception("Could not find the product!");
    }

    List<Substance> substanceInfos = new List<Substance>();

    // string[] substanceNames = new string[] { product.Substance1, product.Substance2, product.Substance3, product.Substance4 };
    Console.WriteLine($"ProductName: {product.ProductName}");

    return product;
}

This line:

Product product = _productRepository.GetProductDataByName(ProductName);

leads to first endpoint. The logic I want to implement:

1. Send request to this endpoint with drug name
2. Drug is being unfolded into substances.
3. For all the substances, the request is sent to get the info about the substance
4. The list of info about substances is returned.

So I sent request /ApapExtra and I want to get:

{
    "substanceId": 4,
    "name": "Paracetamolum",
    "effect": "Analgesic"
}
{
    "substanceId": 4,
    "name": "Coffeinum",
    "effect": "Analgesic"
}

because it consists of these ingredients.

The problem is with:

string[] substanceNames = new string[] { product.Substance1, product.Substance2, product.Substance3, product.Substance4 };

because I get:

Possible null reference assignment.CS8601

even though I have in models ? next to the field names.

How to fix this problem? Or how to solve it in a better way?