Bug 182673 No default value error message prompts incorrectly
Steps to reproduce: 1. New a report parameter; 2. Choose control type as Combo; 3. Choose parameter as dynamic type; Expected result: As the isRequired is false by default, parameter's default value can be null value. There should be no error message about no default value prompt. Actual result; Error messages prompts
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
importValue = new Button( buttonBar, SWT.PUSH );
		importValue.setText( BUTTON_LABEL_IMPORT );
		setButtonLayoutData( importValue );
		
		importValue.setEnabled( !inputParameter.getModuleHandle( )
				.getVisibleDataSets( )
				.isEmpty( ) );
		importValue.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				boolean defaultValueRemoved = true;
				String type = getSelectedDataType( );
				List choices = new ArrayList( );
				Map labelMap = new HashMap( );
				for ( Iterator iter = choiceList.iterator( ); iter.hasNext( ); )
				{
					SelectionChoice choice = (SelectionChoice) iter.next( );
					choices.add( choice.getValue( ) );
					if ( choice.getLabel( ) != null )
					{
						labelMap.put( choice.getValue( ), choice.getLabel( ) );
					}
				}
				ImportValueDialog dialog = new ImportValueDialog( type, choices );
				if ( dialog.open( ) == OK )
				{
					String[] importValues = (String[]) dialog.getResult( );
					choiceList.clear( );
					for ( int i = 0; i < importValues.length; i++ )
					{