Support for optional object properties

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.