Bug 167545 Copy a cascading parameter group and paste it to another parameter group causes an exception thrown
Steps to reproduce: 1.Copy a cascading parameter group using short cut key "Ctrl+x"/"Ctrl+c", or choosing context menu "Cut"/"Copy"; 2.Paste it to another parameter group using short cut key "Ctrl+v", or choosing context menu "Paste"; Expected result: The source one is pasted in the destination. Actual result: An exception thrown org.eclipse.birt.report.model.api.command.ContentException: The Cascading Parameter Group("Source") is not allowed in the slot (parameters) of Parameter Group("Destination").
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
*            a String value.
	 * @return non-null value.
	 */
	public static String resolveNull( String value )
	{
		return value == null ? "" : value; 
	}
	/**
	 * Converts the RGB object value to a String, the String format is "r,g,b",
	 * no quotation marks.
	 * 
	 * @param rgb
	 *            RGB value.
	 * @return String value.
	 */
	public static String getRGBText( RGB rgb )
	{
		if ( rgb != null )
		{
			return rgb.red + "," + rgb.green + "," + rgb.blue; 
		}
		return ""; 
	}
	/**
	 * Converts the String value to an RGB object value, the String format is
	 * "r,g,b", no quotation marks.
	 * 
	 * @param val
	 *            String value.
	 * @return RGB value.