"regular" constraint doesn't accept empty array

ICF.regular() throws when I pass it an empty IntVar array:

``` clojure
ArrayIndexOutOfBoundsException 0 org.chocosolver.solver.constraints.Propagator. (Propagator.java:140)
```

I assumed that if I passed in an empty array, the constraint would succeed if and only if the automaton accepts the empty string. Is that not a desired feature in Choco or is this a bug?