V operator [](
Object key
)

Returns the value for the given key or null if key is not in the map.

Some maps allows keys to have null as a value, For those maps, a lookup using this operator does cannot be used to distinguish between a key not being in the map, and the key having a null value. Methods like containsKey or putIfAbsent can be use if the distinction is important.

Source

/**
 * Returns the value for the given [key] or null if [key] is not in the map.
 *
 * Some maps allows keys to have `null` as a value,
 * For those maps, a lookup using this operator does cannot be used to
 * distinguish between a key not being in the map, and the key having a null
 * value.
 * Methods like [containsKey] or [putIfAbsent] can be use if the distinction
 * is important.
 */
V operator [](Object key);