Returns <code>true</code> if the receiver does not cover any
area in the (x, y) coordinate plane, and <code>false</code> if
the receiver does cover some area in the plane.
<p>
A rectangle is considered to <em>cover area</em> in the
(x, y) coordinate plane if both its width and height are
non-zero.
</p>
@return <code>true</code> if the receiver is empty, and <code>false</code> otherwise
Returns <code>true</code> if the receiver does not cover any area in the (x, y) coordinate plane, and <code>false</code> if the receiver does cover some area in the plane. <p> A rectangle is considered to <em>cover area</em> in the (x, y) coordinate plane if both its width and height are non-zero. </p>
@return <code>true</code> if the receiver is empty, and <code>false</code> otherwise