‘is null’

The unary postfix operator ‘is null’ is used to check whether a value is explicitly set to JSON null in JsonQL expressions. It returns a boolean result (true or false).

Operator Priority: 300

Operator Operands

  • Operand 1:

    • Type: any valid JsonQL expression (including invalid path).

    • Description: The value to be checked for JSON null.

Evaluation Rules

The is null operator follows these evaluation rules:

  • JSON null value: Returns true if the operand evaluates to a JSON null value

  • Non-null values: Returns false for any non-null value (including numbers, strings, booleans, objects, and arrays)

  • Invalid paths: Returns false for invalid paths (use is undefined to check for invalid paths)

  • Missing values from queries: Returns false even when a query returns no results (e.g., First() with no matches)

Important

The is null operator only returns true when a JSON path explicitly references a null value. It does not return true for:

  • Invalid or non-existent paths

  • Empty query results

  • Undefined values

Use the is undefined operator to check for these cases.

Examples

{
  "Comment_Operator_is_null_1": "(invalid.path is null) evaluates to false. For invalid path check use 'is undefined' operator",
  "Operator_is_null_1": "$value(invalid.path is null == false)",
  "Operator_is_null_2": "$value(NullValue is null)",
  "Operator_is_null_3": "$value(Int1 is null == false)",
  "Operator_is_null_5": "$value(Companies.Select(c => c.Employees).First() is null == false)",

  "Comment_Operator_is_null_6_1": "Even though the query below results in no employee being selected. The value is not null",
  "Comment_Operator_is_null_6_2": "'is null' succeeds if there is JsonPath with null value.",
  "Comment_Operator_is_null_6_3": "'Use 'is undefined' instead to check if query resulted in any value",
  "Operator_is_null_6": "$value(Companies.Select(c => c.Employees).First(e => e.Age > 200) is null == false)"
}