A DESCRIPTION OF THE PROBLEM :
Example of toMap() method indicates to use Funcitons.identity() method instead of Function.identity(). Notice that "s" is not required at the end of "Function".

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Example of toMap() method indicates to use Funcitons.identity() method.
ACTUAL -
Should use Function.identity(). Notice that "s" is not required at the end of "Function".

URL OF FAULTY DOCUMENTATION :
https://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html