Bug 182190 [StatusHandling] [Wizards] getControl assert on wizard page has no message
M6 If you forget to set the control on your wizard page our assert gives no feedback. We need an error message.
bundles/org.eclipse.jface/src/org/eclipse/jface/wizard/WizardDialog.java
*/
    protected void nextPressed() {
        IWizardPage page = currentPage.getNextPage();
        if (page == null) {
            
            return;
        }
        
        showPage(page);
    }
    
    /**
	 * Notifies page changing listeners and returns result of page changing
	 * processing to the sender.
	 * 
	 * @param eventType
	 * @return <code>true</code> if page changing listener completes
	 *         successfully, <code>false</code> otherwise
	 */
    private boolean doPageChanging(IWizardPage targetPage){
    	PageChangingEvent e = new PageChangingEvent(this, getCurrentPage(), targetPage);
		firePageChanging(e);
		
		return e.doit;
    }
    /**
     * Checks whether it is alright to close this wizard dialog
     * and performed standard cancel processing. If there is a
     * long running operation in progress, this method posts an
     * alert message saying that the wizard cannot be closed.