Please make value 0 and "0" settable for IronCache

I have tried using  

    putItem("cacheName", "key1", 0) to set the initial value to 0.

This results in an InvalidArgumentException:

    public function setValue($value) {
        if(empty($value)) {
            throw new InvalidArgumentException("Please specify a value");
        } else {
            $this->value = $value;
        }
    }

This is a very common thing to do when you set up a cache to be used as an incremental counter using incrementItem("cacheName", "key1", 1);

Since it seems like you need an existing value for "key1" to use the increment function we need to instantiate it as something, and 0 is probably the best value.

`empty()` in PHP considers 0 and "0" to be true. 

I have the change I made and it allows both 0 and "0" to be set as cache values. Only setting it to 0 will allow for incrementing it but that should be OK. I don't think it makes sense to not be able to set the value as 0 or "0" in a cache solution so I hope this will be implemented.