Bits of .NET

Validation throwing generic ‘Value cannot be null’ messages? CallerArgumentExpression shows which argument failed.

Old Generic Message:

public void ProcessUser(User user)
{
    if (user == null)
        throw new ArgumentNullException(nameof(user));
    
    // Error: "user cannot be null" - not very helpful in complex code
}

With CallerArgumentExpression:

public void ThrowIfNull(T value, 
    [CallerArgumentExpression("value")] string? paramName = null)
{
    if (value == null)
        throw new ArgumentNullException(paramName, 
            $"Argument '{paramName}' cannot be null");
}

public void ProcessUser(User user)
{
    ThrowIfNull(user);  
    // Error: "Argument 'user' cannot be null"
    
    ThrowIfNull(user.Settings?.Profile);
    // Error: "Argument 'user.Settings?.Profile' cannot be null"
    // Shows exact expression that was null!
}

Debugging becomes way easier!