How to differentiate null and false in JMESPath?

From a JSON object, I want to return true if a key is missing, false otherwise.
How to achieve this?

1. First case, the key is defined: And the value is false

   {"my_key": false}
   

   The expression my_key will return false.

   And the value is a number:

   {"my_key": 123}
   

   The expression my_key will return 123.

2. Second case:

   {"my_other_key": false}
   

   The expression my_key would now return null.

I need an expression which would work with both cases, returning false (or other values) in the first case and true in the second one.

The built-in function not_null could be good, but, it treats false and null equally.

The expression you are looking for would uses a conditional "or" and can be expressed this way:

my_key == null || my_key

Simply put, it tells JMESPath to return either

• the result of the test my_key == null, which would be true only if the value of my_key is strictly equal to null
• or — so, if the test my_key == null result in a false — the value of my_key

Using it on:

• the JSON object

  {"my_key": false}
  

  Would return false
• the JSON object

  {"my_key": 123}
  

  Would return 123
• the JSON object

  {"my_other_key": false}
  

  Would return true