Specifies whether records with null values are indexed.
| Constant | Value | Description |
| adIndexNullsAllow | 0 | The index does allow entries in which the key columns are null. If a null value is entered in a key column, the entry is inserted into the index. |
| adIndexNullsDisallow | 1 | Default. The index does not allow entries in which the key columns are null. If a null value is entered in a key column, an error will occur. |
| adIndexNullsIgnore | 2 | The index does not insert entries containing null keys. If a null value is entered in a key column, the entry is ignored and no error occurs. |
| adIndexNullsIgnoreAny | 4 | The index does not insert entries where some key column has a null value. For an index having a multi-column key, if a null value is entered in some column, the entry is ignored and no error occurs. |