C# adding string + null doesn't throw an error?

Question

As a programmer I would have expected this to throw an exception. Is there a reason why it treats null as ""?

string s = "hello";
string t = null;

Console.WriteLine(s + t);

Output:

hello

Just to emphasise my question, do you know why the decision to turn null into String.Empty was made? I was expecting some string to be added but there was a problem further back where it wasn't retrieving it properly and it came back with null. The problem went unnoticed!

Here's a pseudocode of why I think it is bad (and why I was shocked to discover no error):

You can assume I overloaded ToString to give the name of the person or details about them.

Person p = PersonDatabase.GetForName("Jimmy Gibbs");

Console.WriteLine("Name is: " + p.ToString());

Throws an exception because p is null

String p = PersonDatabase.GetForName("Jimmy Gibbs").Name;

Console.WriteLine("Name is: " + p);

Doesn't throw an exception, even though p is null (it treats it as "").

(If you want to be picky and say I won't be able to get Name as GetforName will be null, think of it as this:)

String p = PersonDatabase.GetNameFromID(1234); // Returns a string or null if not found

Console.WriteLine("Name is: " + p);

(If you use this value in a list or array you'll end up with a blank entry which is what broke for me, it was creating javascript and trying to get element by ID of "")

Answer 1

From the C# Language Specification:

7.8.4 Addition operator

String concatenation:

string operator +(string x, string y); string operator +(string x, object y); string operator +(object x, string y);

These overloads of the binary + operator perform string concatenation. If an operand of string concatenation is null, an empty string is substituted. Otherwise, any non-string argument is converted to its string representation by invoking the virtual ToString method inherited from type object. If ToString returns null, an empty string is substituted.