Bug 153405 Null parameter value is inconsistent between designer and preview
Description: Null parameter value is inconsistent between designer and preview Steps to reproduce: 1. New a report parameter, list-box, tick AllowNull. 2. Click New button, click OK without input anything. 3. Drag the parameter to Layout and preview Actual result: After step2, display text is "Null" and value is empty. However, when preview, the display text is "Null Value". Expected result: Display text and value should be consistent between Edit Parameter Dialog in Layout and Parameter dialog during preview.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
{
		boolean isEnable = true;
		SelectionChoice selectedChoice = null;
		if ( valueTable.getSelection( ).isEmpty( ) )
		{
			isEnable = false;
		}
		else
		{
			selectedChoice = (SelectionChoice) ( (IStructuredSelection) valueTable.getSelection( ) ).getFirstElement( );
			
			
			
			
		}
		boolean isDefault = isEnable && isDefaultChoice( selectedChoice );
		if ( isDefault )
		{
			changeDefault.setText( BUTTON_LABEL_REMOVE_DEFAULT );
		}
		else
		{
			changeDefault.setText( BUTTON_LABEL_SET_DEFAULT );
		}
		changeDefault.setSelection( isDefault );
		changeDefault.setEnabled( isEnable );
	}
	private void updateButtons( )
	{
		boolean canFinish = !StringUtil.isBlank( nameEditor.getText( ) );