Returns the value at the specified key in the current
public function get( Tk $k, ): ?Tv;
If the key is not present, null is returned. If you would rather have an
exception thrown when a key is not present, then use
$k- the key from which to retrieve the value.
?Tv- The value at the specified key; or
nullif the key does not exist.
Map::get for usage examples.