Описание тега null-conditional-operator

A Safe navigation operator used to test for null before performing a member access (?.) or index (?[]) operation.

These operators help you write less code to handle null checks, especially for descending into data structures.

C#:

int? length = customers?.Length; // null if customers is null 
Customer first = customers?[0];  // null if customers is null
int? count = customers?[0]?.Orders?.Count();  // null if customers, the first customer, or Orders is null

VB:

Dim length = customers?.Length  ‘’ null if customers is null
Dim first as Customer = customers?(0);  ‘’ null if customers is null
Dim count as Integer? = customers?[0]?.Orders?.Count();  // null if customers, the first customer, or Orders is null

MSDN.