If not null, a plain object with properties:
     type                                    [type: String]                          - type of cell
     rowOrdinals                             [type: Array]                           - the row tuple ordinals
     columnOrdinals                          [type: Array]                           - the column tuple ordinals
     nodes                                   [Type: Array]                           - selected nodes    
     link                                    [Type: Object, mayBeNull: true]         - selected link