8025690: Default FileHandler constructor doesn't throw NullPointerException if pattern is empty and count > 1

[Daniel Fuchs]

Hi,

Please find below a fix for

8025690: Default FileHandler constructor doesn't
          throw NullPointerException if pattern is empty and count > 1
https://bugs.openjdk.java.net/browse/JDK-8025690

The default constructor of FileHandler is specified to throw
a NullPointerException if the pattern property string is an
empty string.
(see 
<http://docs.oracle.com/javase/8/docs/api/java/util/logging/FileHandler.html#FileHandler-->) 

However it strangely does so only when count=1

The fix adds an additional check in openFiles() to verify that
the pattern is not empty. At this point the other constructors
(which take a pattern as parameter) will already have thrown an
IAE if the pattern was empty (or an NPE if it was null).

http://cr.openjdk.java.net/~dfuchs/webrev_8025690/webrev.00

best regards,

-- daniel