Round #743

Throw an ArgumentNullException if a parameter is null.

### Throwing ArgumentNullException in C# You can throw an `ArgumentNullException` in C# using the following code: ```csharp public void MyMethod(object parameter) { if (parameter == null) { throw new ArgumentNullException(nameof(parameter)); } // Rest of the method implementation } ``` In this example, `nameof(parameter)` is used to get the name of the parameter as a string. This is a good practice because it allows the compiler to check the parameter name and provides better support for refactoring. ### Best Practices * Always specify the parameter name when throwing an `ArgumentNullException`. This helps with debugging and error reporting. * Consider using the `ArgumentNullException` constructor that takes two parameters: the parameter name and a custom error message. ```csharp throw new ArgumentNullException(nameof(parameter), "Parameter cannot be null"); ``` ### Example Use Case Here's an example of a method that throws an `ArgumentNullException` if the input string is null: ```csharp public void PrintString(string input) { if (input == null) { throw new ArgumentNullException(nameof(input), "Input string cannot be null"); } Console.WriteLine(input); } ``` You can call this method like this: ```csharp try { PrintString(null); } catch (ArgumentNullException ex) { Console.WriteLine(ex.Message); } ``` This will output: "Input string cannot be null"

```csharp using System; public class ParameterValidator { public static void ValidateParameter(object parameter, string parameterName) { if (parameter == null) { throw new ArgumentNullException(parameterName, $"{parameterName} cannot be null."); } } } public class Program { public static void Main() { try { object obj = null; ParameterValidator.ValidateParameter(obj, nameof(obj)); } catch (ArgumentNullException ex) { Console.WriteLine(ex.Message); } } } ``` This code defines a `ParameterValidator` class with a `ValidateParameter` method that checks if a given parameter is null. If the parameter is null, it throws an `ArgumentNullException` with a message indicating the name of the parameter that is null. In the `Main` method, we demonstrate how to use this validation method. We create a null object and pass it to the `ValidateParameter` method along with its name. Since the object is null, the method throws an `ArgumentNullException`, which we catch and print to the console. The `nameof` operator is used to get the name of the parameter as a string, which is then passed to the `ValidateParameter` method. This approach helps to avoid magic strings and makes the code more maintainable.