A DESCRIPTION OF THE PROBLEM :
Functions.identity()

Functions is wrong Lib

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Function.identity()
ACTUAL -
Functions.identity()

URL OF FAULTY DOCUMENTATION :
https://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html#toMap-java.util.function.Function-java.util.function.Function-