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
initFormatField( );
	}
	private void switchParamterType( )
	{
		clearArea( valueArea );
		lastControlType = null;
		if ( isStatic( ) )
		{
			switchToStatic( );
		}
		else
		{
			switchToDynamic( );
		}
		buildControlTypeList( getSelectedDataType( ) );
		valueArea.layout( );
		initValueArea( );
		updateCheckBoxArea( );
	}
	private void switchToCheckBox( )
	{
		createLabel( valueArea, LABEL_DEFAULT_VALUE );
		defaultValueChooser = new Combo( valueArea, SWT.READ_ONLY | SWT.BORDER );
		defaultValueChooser.add( CHOICE_NO_DEFAULT );
		defaultValueChooser.add( BOOLEAN_TRUE );
		defaultValueChooser.add( BOOLEAN_FALSE );
		defaultValueChooser.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		defaultValueChooser.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{