It means that the value type in question is a nullable type . Nullable types are instances of the System. Nullable struct. A nullable type can represent the correct range of values for its underlying value type, plus an additional null value.22 Nis 2010
Read moreWhat is the question mark in Dart?
Dart offers some handy operators for dealing with values that might be null. One is the ??= assignment operator, which assigns a value to a variable only if that variable is currently null: int a; // The initial value of a is null.
Read moreWhat does a question mark after a variable mean?
The question mark in JavaScript is commonly used as conditional operator — called ternary operator when used with a colon (:) and a question mark (?) — to assign a variable name conditionally .
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