CA1062: Validate parameter is non-null before using it

When you have a public method that isn’t null checking its parameters, then you’ll get the CA1062 code analysis warning.

For example, the following code isn’t null checking the movieRepository parameter:

public class StreamingService
{
	public void LogMovies(MovieRepository movieRepository)
	{
		foreach (var movie in movieRepository.GetMovies())
		{
			Console.WriteLine(movie.Name);
		}
	}
}
Code language: C# (cs)

This results in the CA1062 code analysis warning:

CA1062 In externally visible method ‘void StreamingService.LogMovies(MovieRepository movieRepository)’, validate parameter ‘movieRepository’ is non-null before using it. If appropriate, throw an ArgumentNullException when the argument is null or add a Code Contract precondition asserting non-null argument.

There are a few good options for solving this problem: check for null or suppress the warning. You’ll have to decide which option makes sense in your situation.

Option 1 – Check for null

It’s generally a good idea to null check your parameters. If the parameter is null, you can throw an exception, return some special result, or perhaps use a default value instead.

In this example, it’s throwing an ArgumentNullException.

public void LogMovies(MovieRepository movieRepository)
{
	if (movieRepository == null)
		throw new ArgumentNullException(nameof(movieRepository));


	foreach (var movie in movieRepository.GetMovies())
	{
		Console.WriteLine(movie.Name);
	}
}
Code language: C# (cs)

Option 2 – Suppress the warning

Let’s say you are sure the parameter won’t be null. Or if it’s null, you’re OK with it blowing up and throwing a NullReferenceException. In this case, you can suppress the warning with a pragma, like this:

public void LogMovies(MovieRepository movieRepository)
{
#pragma warning disable CA1062 // Validate arguments of public methods
	foreach (var movie in movieRepository.GetMovies())
	{
		Console.WriteLine(movie.Name);
	}
#pragma warning restore CA1062 // Validate arguments of public methods

}
Code language: C# (cs)

I wouldn’t recommend suppressing this code analysis rule for the entire project. You should take it on a case by case basis and determine if it’s ok to suppress it for the specific scenario.

Note: You can also add [NotNull] to the parameter to ignore the warning. If you’re using FxCop, this will make it ignore the problem. [NotNull] does not seem to make any difference when using .NET Analyzers (this might be a bug).