Null pointer exceptions and warnings

Simple code

I am developer so let's start with following C# code:

    public static void Main()
    {
        var sampleList = GetSamples();
        if (sampleList.FirstOrDefault().StartsWith("I"))
        {
            Console.WriteLine("First element starts with I");
        }
        else
        {
            Console.WriteLine("First element doesn't start with I");
        }
    }

It compile without any warnings, which is quite cool, But will it work without problems? Of course it depends on GetSamples function. But it should, isn't it?

Full implementation

So let's extend above code to full implementation:

    static readonly Random Random = new Random();
    static List<string> GetSamples()
    {
        if (Random.Next(100) > 2)
        {
            return new List<string>{"I"};
        }
        return new List<string>();
    }
    public static void Main()
    {
        var sampleList = GetSamples();
        if (sampleList.FirstOrDefault().StartsWith("I"))
        {
            Console.WriteLine("First element starts with I");
        }
        else
        {
            Console.WriteLine("First element doesn't start with I");
        }
    }

Now it starts to look tricky and dangerous. But again you will don't have any warning in Visual Studio.

Resharper to the rescue

If you use R# you will see following warning:

Using Alt+Entershortcut generate simple fix:

var firstOrDefault = sampleList.FirstOrDefault();
if (firstOrDefault != null && firstOrDefault.StartsWith("I"))
{
   Console.WriteLine("First element starts with I");
}
else
{
   Console.WriteLine("First element doesn't start with I");
}

And we are safe now :)

... but it doesn't show everything

But imagine that instead of FirstOrDefault() the developer used First(), so the above if will be following:

if (sampleList.First().StartsWith("I"))

In above case it won't be any warning even in Resharper :(

Menu