putIfAbsent abstract method

FutureOr<V?> putIfAbsent(
  1. K key,
  2. V? absentValue
)

Sets the absentValue of key if it's null, and returns it. If the key value is already define and is NOT null, returns the previous value.

Implementation

FutureOr<V?> putIfAbsent(K key, V? absentValue);