A DESCRIPTION OF THE PROBLEM :
I think there is a typo in the Javadoc of the parse method of java.time.Duration: a "a" should be used before "long" and not a "an".

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The number of days, hours and minutes must parse to a long.
ACTUAL -
The number of days, hours and minutes must parse to an long.

URL OF FAULTY DOCUMENTATION :
https://docs.oracle.com/javase/8/docs/api/java/time/Duration.html#parse-java.lang.CharSequence-