Avoiding NullReferenceException in Request.QueryString

Question

This code throws a NullReferenceException if mode is not specified in the pages query string:

bool isAdvancedMode = Request.QueryString["mode"].Equals("advanced");

This is how I work around this:

bool isAdvancedMode = (Request.QueryString["mode"] + "").Equals("advanced");

Is this standard practise, or a hack?

Answer 1

You can use the null-coalescing operator:

bool isAdvancedMode = (Request.QueryString["mode"] ?? String.Empty).Equals("advanced");

Edit: If you want to re-use this logic, try this extension method:

public static bool EqualIfExists(this string source, string comparison)
{
    return source != null && source.Equals(comparison);
}

Request.QueryString["mode"].EqualIfExists("advanced")

Add more overrides to match Equals signature. I'm not sure if this is a good name (I think it is not).

Answer 2

Well, I would recommend this instead:

bool isAdvancedMode = (Request.QueryString["mode"] ?? "").Equals("advanced");

In fact, this is what your code compiles to (Nearer the bottom, but it's a good read so I'd read it all). Yours is good practice, but this is a bit more clear.