Returns the receiver's parent, which must be a <code>Shell</code>
or null.
@return the receiver's parent
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Returns the receiver's parent, which must be a <code>Shell</code> or null.
@return the receiver's parent
@exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>