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
{
				e.doit = ( "0123456789\0\b\u007f".indexOf( e.character ) != -1 ); 
			}
		} );
		Label values = new Label( limitArea, SWT.NULL );
		values.setText( Messages.getString( "ParameterDialog.Label.values" ) ); 
		values.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		
		createLabel( displayOptionSection, null ); 
		Composite checkBoxArea = new Composite( displayOptionSection, SWT.NONE );
		checkBoxArea.setLayout( UIUtil.createGridLayoutWithoutMargin( 2, false ) );
		checkBoxArea.setLayoutData( new GridData( GridData.FILL_BOTH ) );
		isRequired = new Button( checkBoxArea, SWT.CHECK );
		isRequired.setText( CHECKBOX_ISREQUIRED );
		addCheckBoxListener( isRequired, CHECKBOX_ISREQUIRED );
		doNotEcho = new Button( checkBoxArea, SWT.CHECK );
		doNotEcho.setText( CHECKBOX_DO_NOT_ECHO );
		addCheckBoxListener( doNotEcho, CHECKBOX_DO_NOT_ECHO );
		isHidden = new Button( checkBoxArea, SWT.CHECK );
		isHidden.setText( CHECKBOX_HIDDEN );
		addCheckBoxListener( isHidden, CHECKBOX_HIDDEN );
		needSort = new Button( checkBoxArea, SWT.CHECK );
		needSort.setText( CHECKBOX_SORT );
		addCheckBoxListener( needSort, CHECKBOX_SORT );
	}
	private void createValuesDefineSection( Composite composite )
	{
		Group valuesDefineSection = new Group( composite, SWT.NONE );
		valuesDefineSection.setText( LABEL_LIST_OF_VALUE );
		valuesDefineSection.setLayout( new GridLayout( 2, false ) );