Sets the default menu item to the argument or removes
the default emphasis when the argument is <code>null</code>.
@param item the default menu item or null
@exception IllegalArgumentException <ul>
<li>ERROR_INVALID_ARGUMENT - if the menu item has been disposed</li>
</ul>
@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>
Sets the default menu item to the argument or removes the default emphasis when the argument is <code>null</code>.
@param item the default menu item or null
@exception IllegalArgumentException <ul> <li>ERROR_INVALID_ARGUMENT - if the menu item has been disposed</li> </ul> @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>