What is Safe Navigation Operator in Salesforce ?

Safe Navigation Operator is introduced in Salesforce Apex Winter Release 21 to Avoid Null Pointer Exceptions.
Example :-
For example :-
String profileUrl = null;
if (user.getProfileUrl() != null) {
profileUrl = user.getProfileUrl().toExternalForm();
}
/ New code using the safe navigation operator
<b role=”presentation” style=”font-family: inherit; font-size: inherit;”>
String profileUrl = user.getProfileUrl()?.toExternalForm();