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
if ( canFinish )
		{
			if ( errorMessageLine != null && !errorMessageLine.isDisposed( ) )
			{
				canFinish = ( errorMessageLine.getImage( ) == null );
			}
			if ( columnChooser != null && !isStatic( ) )
			{
				canFinish &= ( getExpression( columnChooser.getText( ) ) != null );
			}
		}
		getOkButton( ).setEnabled( canFinish );
	}
	private void updateCheckBoxArea( )
	{
		
		if ( ( DesignChoiceConstants.PARAM_CONTROL_TEXT_BOX.equals( getSelectedControlType( ) )
				|| PARAM_CONTROL_LIST.equals( getSelectedControlType( ) ) || PARAM_CONTROL_COMBO.equals( getSelectedControlType( ) ) )
				&& DesignChoiceConstants.PARAM_TYPE_STRING.equals( getSelectedDataType( ) ) )
		{
			allowBlank.setEnabled( true );
		}
		else
		{
			allowBlank.setEnabled( false );
		}
		
		if ( DesignChoiceConstants.PARAM_CONTROL_TEXT_BOX.equals( getSelectedControlType( ) ) )
		{
			doNotEcho.setEnabled( true );