TYPO3 Core

I have a flexform with a select and want to have two options (nothing and all) plus values from the database. If I select the second (fixed value) after saving the first value is selected again. Here is my code:

                    <settings.myfield>
                        <TCEforms>
                            <label>My label</label>
                            <config>
                                <type>select</type>
                                <renderType>selectSingle</renderType>
                                <items>
                                    <numIndex index="0">
                                        <numIndex index="0">---</numIndex>
                                        <numIndex index="1"></numIndex>
                                    </numIndex>
                                    <numIndex index="1">
                                        <numIndex index="0">Alle</numIndex>
                                        <numIndex index="1">all</numIndex>
                                    </numIndex>
                                </items>
                                <foreign_table>tablename</foreign_table>
                                <foreign_table_where>
                                ...
                                </foreign_table_where>
                            </config>
                        </TCEforms>
                    </settings.myfield>