Conformance Check: Promise Rejections Must be Caught

I'd like to enforce that all promises have rejections caught. Either:

``` js
promiseReturningFunction()
.then(resFn, rejFn)
.then(resFn) //warning here
.then(resFn, rejFn);
```

or

``` js
promiseReturningFunction()
.then(resFn, rejFn)
.then(resFn) //no warning here - it's caught
.then(resFn, rejFn)
.catch(rejFn);
```

I could also see this as a lint check rather than a conformance requirement.