Bug 180864 Change Allow Null option in Cascading Group.[0705]
Description: Change Allow Null option in Cascading Group. Build number:2.2.0.v20070404 Steps to reproduce: 1. New a cascading group and add sub parameter. Expected result: Is Required option in cascading group definition dialog. Actual result: Allow null value option in Cascading Group definition dialog Error log:N/A
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
.findChoice( DesignChoiceConstants.STRING_FORMAT_TYPE_UNFORMATTED )
					.getDisplayName( );
		}
		else
		{
			displayFormat = choiceSet.findChoice( formatCategroy )
					.getDisplayName( );
			if ( isCustom( ) )
			{
				displayFormat += ":  " + formatPattern; 
			}
		}
		formatField.setText( "" + displayFormat ); 
		changeFormat.setEnabled( choiceSet != null );
		if ( selectedParameter != null )
		{
			doPreview( isCustom( ) ? formatPattern : formatCategroy );
		}
	}
	private boolean isCustom( )
	{
		if ( DesignChoiceConstants.STRING_FORMAT_TYPE_CUSTOM.equals( formatCategroy )
				|| DesignChoiceConstants.NUMBER_FORMAT_TYPE_CUSTOM.equals( formatCategroy )
				|| DesignChoiceConstants.DATETIEM_FORMAT_TYPE_CUSTOM.equals( formatCategroy ) )
		{
			return true;
		}
		return false;
	}
	private void doPreview( String pattern )