Returns a new rectangle which represents the union of
the receiver and the given rectangle.
<p>
The union of two rectangles is the smallest single rectangle
that completely covers both of the areas covered by the two
given rectangles.
</p>
@param rect the rectangle to perform union with
@return the union of the receiver and the argument
@exception IllegalArgumentException <ul>
<li>ERROR_NULL_ARGUMENT - if the argument is null</li>
</ul>
Returns a new rectangle which represents the union of the receiver and the given rectangle. <p> The union of two rectangles is the smallest single rectangle that completely covers both of the areas covered by the two given rectangles. </p>
@param rect the rectangle to perform union with @return the union of the receiver and the argument
@exception IllegalArgumentException <ul> <li>ERROR_NULL_ARGUMENT - if the argument is null</li> </ul>
@see #add(Rectangle)