c# - Why is the result of adding two null strings not null?

Question

(This question already has answers here): question from:https://stackoverflow.com/questions/21778406/why-is-the-result-of-adding-two-null-strings-not-null

Answer 1

From MSDN:

In string concatenation operations, the C# compiler treats a null string the same as an empty string,

Even though xyz is null, calling the += operator (which is converted to a call to the + operator (*)) on it does not throw a NullReferenceException because it's a static method. In pseudo code:

xyz = String.+(null, null);

The implementation will then interpret this as if it was

xyz = String.+("", "");

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(*) Section §7.17.2 of the C# specification:

An operation of the form x op= y is processed by applying binary operator overload resolution (§7.3.4) as if the operation was written x op y.