A dummy value (-9999) indicates "No Value" for some points in a Point Shapefile Feature Class. The symbology for those points is defined as a grey dot in Layer Properties > Symbology > Classify > Exlusion > Legend. However, this grey dot becomes the lowermost symbol and, by this, covers the other points which do have values. The grey dot can not be accessed by Layer Properties > Symbology > Advanced > Symbol Levels. How should I proceed in order to make the grey dot appear in the back, i.e. as the uppermost symbol?