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
{
					inputParameter.setLabelExpr( "" );
				}
				else
				{
					inputParameter.setLabelExpr( getExpression( displayTextChooser.getText( ) ) );
				}
			}
			
			inputParameter.setHelpText( UIUtil.convertToModelString( helpTextEditor.getText( ),
					false ) );
			
			inputParameter.setCategory( formatCategroy );
			inputParameter.setPattern( formatPattern );
			if ( isStatic( )
					&& ( PARAM_CONTROL_COMBO.equals( getSelectedControlType( ) ) || DesignChoiceConstants.PARAM_CONTROL_RADIO_BUTTON.equals( getSelectedControlType( ) ) )
					&& !containValue( null, defaultValue, COLUMN_VALUE ) )
			{
				defaultValue = null;
			}
			
			if ( dirtyProperties.containsKey( CHECKBOX_HIDDEN ) )
			{
				inputParameter.setHidden( getProperty( CHECKBOX_HIDDEN ) );
			}
			if ( dirtyProperties.containsKey( CHECKBOX_ALLOW_NULL ) )
			{
				inputParameter.setAllowNull( getProperty( CHECKBOX_ALLOW_NULL ) );
			}
			if ( allowBlank.isEnabled( ) )