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
{
			type = DesignChoiceConstants.PARAM_CONTROL_TEXT_BOX;
		}
		else if ( DesignChoiceConstants.PARAM_CONTROL_LIST_BOX.equals( inputParameter.getControlType( ) ) )
		{
			if ( inputParameter.isMustMatch( ) )
			{
				
				type = PARAM_CONTROL_LIST;
			}
			else
			{
				
				type = PARAM_CONTROL_COMBO;
			}
		}
		else
		{
			type = inputParameter.getControlType( );
		}
		return type;
	}
	private String getSelectedDataType( )
	{
		String type = null;
		if ( StringUtil.isBlank( dataTypeChooser.getText( ) ) )
		{
			type = inputParameter.getDataType( );
		}
		else