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
{
	private static final String CHOICE_NO_DEFAULT = Messages.getString( "ParameterDialog.Choice.NoDefault" ); 
	private static final String GROUP_PROPERTIES = Messages.getString( "ParameterDialog.Group.Properties" ); 
	private static final String GROUP_MORE_OPTION = Messages.getString( "ParameterDialog.Group.MoreOption" ); 
	private static final String LABEL_NAME = Messages.getString( "ParameterDialog.Label.Name" ); 
	
	
	private static final String LABEL_DATETIME_PROMPT = "Please enter date values as: MM/DD/YYYY hh:mm:ss AM/PM"; 
	private static final String LABEL_PROMPT_TEXT = Messages.getString( "ParameterDialog.Label.PromptText" ); 
	private static final String LABEL_PARAM_DATA_TYPE = Messages.getString( "ParameterDialog.Label.DataType" ); 
	private static final String LABEL_DISPALY_TYPE = Messages.getString( "ParameterDialog.Label.DisplayType" ); 
	private static final String LABEL_DEFAULT_VALUE = Messages.getString( "ParameterDialog.Label.DefaultValue" ); 
	private static final String LABEL_HELP_TEXT = Messages.getString( "ParameterDialog.Label.HelpText" ); 
	private static final String LABEL_LIST_OF_VALUE = Messages.getString( "ParameterDialog.Label.ListOfValue" ); 	
	private static final String LABEL_VALUES = Messages.getString( "ParameterDialog.Label.Value" ); 
	private static final String LABEL_FORMAT = Messages.getString( "ParameterDialog.Label.Format" ); 
	private static final String LABEL_LIST_LIMIT = Messages.getString( "ParameterDialog.Label.Listlimit" ); 
	private static final String LABEL_NULL = Messages.getString( "ParameterDialog.Label.Null" ); 
	private static final String LABEL_SELECT_DISPLAY_TEXT = Messages.getString( "ParameterDialog.Label.SelectDisplayText" ); 
	private static final String LABEL_SELECT_VALUE_COLUMN = Messages.getString( "ParameterDialog.Label.SelectValueColumn" ); 
	private static final String LABEL_SELECT_DATA_SET = Messages.getString( "ParameterDialog.Label.SelectDataSet" ); 
	private static final String LABEL_PREVIEW = Messages.getString( "ParameterDialog.Label.Preview" ); 
	private static final String CHECKBOX_ALLOW_NULL = Messages.getString( "ParameterDialog.CheckBox.AllowNull" ); 
	private static final String CHECKBOX_ALLOW_BLANK = Messages.getString( "ParameterDialog.CheckBox.AllowBlank" ); 
	private static final String CHECKBOX_DO_NOT_ECHO = Messages.getString( "ParameterDialog.CheckBox.DoNotEchoInput" );