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
valuesDefineSection.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		Composite choiceArea = new Composite( valuesDefineSection, SWT.NONE );
		choiceArea.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		choiceArea.setLayout( UIUtil.createGridLayoutWithoutMargin( 2, true ) );
		staticRadio = new Button( choiceArea, SWT.RADIO );
		staticRadio.setText( RADIO_STATIC );
		staticRadio.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				switchParamterType( );
			}
		} );
		dynamicRadio = new Button( choiceArea, SWT.RADIO );
		dynamicRadio.setText( RADIO_DYNAMIC );
		dynamicRadio.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				switchParamterType( );
			}
		} );
		valueArea = new Composite( valuesDefineSection, SWT.NONE );
		valueArea.setLayout( UIUtil.createGridLayoutWithoutMargin( 2, false ) );
		GridData gd = new GridData( GridData.FILL_BOTH );
		gd.heightHint = 200;
		gd.widthHint = 550;
		gd.horizontalSpan = 2;
		valueArea.setLayoutData( gd );
		createLabel( valuesDefineSection, null );
		errorMessageLine = new CLabel( valuesDefineSection, SWT.NONE );
		GridData msgLineGridData = new GridData( GridData.FILL_HORIZONTAL );