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?

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.
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.

Solution

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: