Source: https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/data-types/null-type/
Documentation version: v5.3.2

# NULL type

The null value represents the absence of a value. It is different from an empty string, the number `0`, or an empty container. NebulaGraph Database Developer Edition uses the `NULL` type during expression type inference when a null value does not yet have a specific material type.

The `NULL` type is an immaterial value type and cannot be used as a node or edge property type.

## View the NULL type

Use the `typeof()` function to view the type of a `NULL` expression:

````
RETURN typeof(NULL)

````

Return:

````
+--------------+
| typeof(NULL) |
+--------------+
| NULL         |
+--------------+

````

## NULL type, null value, and nullability

 | Concept | Example | Meaning
 | `NULL` type | `typeof(NULL)` | The type inferred for a standalone `NULL` expression when no more specific type can be determined from the context
 | Null value | `name = NULL` | Indicates that no value is currently present
 | Nullable type | `name STRING DEFAULT NULL` | The storage location permits a null value
 | Non-nullable type | `id INT64 NOT NULL` | The storage location does not permit a null value

For example:

````
'''
VALUE name STRING = NULL
RETURN typeof(name), name
'''

+--------------+------+
| typeof(name) | name |
+--------------+------+
| STRING       | null |
+--------------+------+

````

The declared type of `name` is `STRING`, and its current value is `NULL`. A null value does not change the declared type of a variable or property to `NULL`.

The same distinction applies to properties:

````
NODE Person (
  LABEL Person {
    id INT64 NOT NULL,
    name STRING DEFAULT NULL,
    PRIMARY KEY (id)
  }
)

````

The type of the `name` property is `STRING`, and `DEFAULT NULL` specifies its default value. You cannot declare a property as `name NULL`.

## Uses of the NULL type

The `NULL` type is primarily used for expression type inference. A standalone `NULL` expression does not contain enough information to determine whether it represents a string, number, or date. When it is used in a context with a specific type, the system handles the null value according to that context.

`NULL` can also occur in container expressions such as lists, sets, and maps. When a container also contains non-null values, the system uses those values to infer the container element type.

## Related operations

- To test whether a value is null, see [NULL predicate](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/fe/predicates/null/).
- For null comparison rules, see [Comparison predicates](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/fe/predicates/comparison/).
- For null conversion rules, see [Cast value expression](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/fe/expressions/cast/).
- For how functions handle null values, see [Null behavior of functions](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/fe/#null_behavior).

Note

Use `IS NULL` or `IS NOT NULL` to test for a null value. Do not use an ordinary equality comparison.