A DESCRIPTION OF THE PROBLEM :
The API document is not mentioning the case that java.utl.regex.Pattern.matcher(input) gets the argument input = null, and the description can be read that the method 'matcher' never raises exceptions. However jre provided by Oracle raises NullPointerException for the case.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
  To be added the 'Throws' paragraph to the 'matcher's description, and be described about the case if input is null.
ACTUAL -
Nothing about the exception is written.

URL OF FAULTY DOCUMENTATION :
http://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html#matcher(java.lang.CharSequence)