Support for optional object properties

[flodaniel]

Let's say we have the following Fact:

{
  "firstName": "John",
  "lastName" : "doe",
  "age"      : 26,
  "address"  : {
    "streetAddress": "naist street",
    "city"         : "Nara",
    "postalCode"   : "630-0192"
  },
  "phoneNumbers": [
    {
      "type"  : "iPhone",
      "number": "0123-4567-8888"
    },
    {
      "type"  : "home",
      "number": "0123-4567-8910"
    }
  ]
}

The following rule snippet should return true in my understanding:

  {
                fact: 'a',
                path: `$..phoneNumbers..title`,
                operator: 'doesNotContain',
                value: 'SOMETITLE'
            },

However this will evaluate to false, as "title" is not present in the object.
The actual use case I have is that the dynamic fact ist an array of objects which can be an empty array sometimes (due to input params for the fact).

Supporting this use case would be very valuable, otherwise additional custom operators are necessary.

[CacheControl]

Some thoughts and notes on this:

What's happening under the hood here is that the path evaluation is returning undefined, because the object property doesn't exist. This is ultimately evaluated as "does undefined not contain "'SOMETITLE'"? which is a non-sensical question; it's like asking "is 'hello' not divisible by 5"?

If the user of the library is configuring a rule this way, it's possible that they made a mistake in the data, rather than them intentionally configuring a non-sensical conditional. Alternatively, as in the use case above, it's possible the user has variable data and is using the conditional to filter out the fact data that doesn't belong.

One solve here is to change the behavior to assume that a negative operators should be considered truthy when given a non-sensical task (breaking change). Alternatively, we might be to make this a configurable option, similar to allowUndefinedFacts (non-breaking).