ReSharper 2018.3 Help

Code Inspection: '??' condition is known to be always null or not null

If you want to assign a value, pass an argument, or return from a method based on the nullability of an identifier, the clearest syntax you can use in these cases is the ?? (null-coalescing) operator.

A null-coalescing expression works as follows. The left-hand operand is evaluated first, and if it is null, the right-hand operand is evaluated and the result becomes the result of the whole expression.

However, redundant null-coalescing expressions produce dead code and impede readability. As it follows from the logic of the ?? operator, using null as the right-hand operand does not make sense. Below, ReSharper suggests removing the right-hand operand null together with the ?? operator, because if the newCategory is null, then null will be assigned to the Category anyway:

Suboptimal code

After the quick-fix

public class Customer { public string Category { get; set; } private void ChangeCategory(string newCategory) { Category = category ?? null; } /* … */ }

public class Customer { public string Category { get; set; } private void ChangeCategory(string newCategory) { Category = category; } /* … */ }

Another situation when the null-coalescing operator is redundant is when the left-hand operand can never be null. In this case, the right-hand operand never gets reached and ReSharper suggests removing the unreachable code:

Suboptimal code

After the quick-fix

string name = "John"; Console.WriteLine(name ?? "empty");

string name = "John"; Console.WriteLine(name);

Last modified: 18 December 2018

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