map
If a value is present, returns an Optional describing (as if by ofNullable) the result of applying the given mapping function to the value, otherwise returns an empty Optional.
If the mapping function returns a null result then this method returns an empty Optional.
Return
an Optional describing the result of applying a mapping function to the value of this Optional, if a value is present, otherwise an empty Optional
Parameters
mapper
the mapping function to apply to a value, if present
the type of the value returned from the mapping function