I have a method that continuously gives me a warning "is not null here".

        StockHolding stockHoldingFiltered = new StockHolding();
        List<StockHolding> stockHoldingsFiltered = new List<StockHolding>();
        IReadOnlyList<StockHolding> stockHoldings = this.GetAll();

        stockHoldingsFiltered = stockHoldings.Where(stckhold =>
            stckhold.PortfolioId.Equals(portfolioId) &&
            stckhold.StockSymbol.Equals(stockSymbol)).ToList();

        if(stockHoldingsFiltered != null)
            stockHoldingFiltered = stockHoldingsFiltered.FirstOrDefault();

        return stockHoldingFiltered;

Warning: 'stockHoldingFiltered' is not null here. CS8600: Converting null literal or possible null value to non-nullable type.

I cannot get this warning to go away. Has anyone run into this and were able to resolve this warning?

CodePudding user response：

This issue is with your if statement. You are doing a null check on a ToList(). The list isn't going to be null, but it can however be empty. Here is your code below to demonstrate this.

void Main()
{
    int portfolioId = 1;
    string stockSymbol = "USD";

    StockHolding stockHoldingFiltered = new StockHolding();
    List<StockHolding> stockHoldingsFiltered = new List<StockHolding>();
    IReadOnlyList<StockHolding> stockHoldings = StockHolding.GetAll();

    stockHoldingsFiltered = stockHoldings.Where(stckhold =>
        stckhold.PortfolioId.Equals(portfolioId) &&
        stckhold.StockSymbol.Equals(stockSymbol)).ToList();

    if (stockHoldingsFiltered != null) // this cannot be null as its returning a list. It might be empty but not null.
    {
        Console.WriteLine("I WASN't NULL, but has no records. Line below will fail.");
        //stockHoldingFiltered = stockHoldingsFiltered.FirstOrDefault();
    }
    
    if(stockHoldingsFiltered.Count > 0)
    {
        Console.WriteLine("I wasnt null but had 0 records. Line below is safe");
        stockHoldingFiltered = stockHoldingsFiltered.FirstOrDefault();
    }

    //return stockHoldingFiltered;
}

// You can define other methods, fields, classes and namespaces here
public class StockHolding
{
    public int PortfolioId { get; set; }
    public string StockSymbol { get; set; }
    
    public static IReadOnlyList<StockHolding> GetAll()
    {
        List<StockHolding> someList = new List<StockHolding>();
        
        return someList;
        
    }
}

This outputs: I WASN't NULL, but has no records. Line below will fail.

So instead of if (stockHoldingsFiltered != null) try using if(stockHoldingsFiltered.Count > 0)

That warning will go away.