Iterator_hasNext

##Improvement in property##
Iterator_hasNext property (https://goo.gl/sO43It) requires a program to guarantee that to call Iterator.hasNext() 
before calling Iterator.next() in order to prevent the NullPointerException triggered when there is no next element in 
the underlying collection without proper debugging information. From our inspection of the monitoring
on 200 open source projects with this property, we found that most false alarms of this property was
triggered because the developer check the validity of calling Iterator.next() by means beside calling Iterator.hasNext(),
typically by calling collection.isEmpty() or collection.size(). We hereby suggest adding such checks as valid
prerequisites for calling Iterator.next() to avoid false alarms.
For example, in compile-testing 
https://github.com/google/compile-testing/blob/51cdab8998ea25210e8d3726982947054f421f94/src/main/java/com/google/testing/compile/TypeEnumerator.java#L102
Iterator_HasNext is violated while the validity of this call is checked by collection.isEmpty(). 
We have seen many similar kind of false alarms in the 200 open source projects we monitored with JavaMOP.