In many cases a String's empty status is tested with `.equals("")`.
However, Java 1.6 added `.isEmpty()` which can be more efficient since
it compares the internal length parameter only for testing. Replace
code using the `.isEmpty()` variant instead.
Some tests for `"".equals(expr)` can be replaced with `expr.isEmpty()`
where it is already known that the `expr` is not null; however,
these have to be reviewed on a case-by-case basis.
Change-Id: I3c6af4d8b7638e757435914ac76cb3a67899a5fd
Signed-off-by: Alex Blewitt <alex.blewitt@gmail.com>