putIfAbsent method Null safety

  1. @override
V putIfAbsent(
  1. K key,
  2. V ifAbsent(
      )
    )
    override

    Throws an UnsupportedError; operations that change the map are disallowed.

    Implementation

    @override
V putIfAbsent(K key, V Function() ifAbsent) => _throw();