A DESCRIPTION OF THE REQUEST :
Add to the beginning of the function: disjoint(Collection<?> c1, Collection<?> c2)

if(c1 == c2) return false; // same collection. All match
if (c1.isEmpty() || c2.isEmpty()) return true; // At least one collection is empty. Nothing will match.




JUSTIFICATION :
This small minor changes will easily improve run-time.
Specially for the case of (c1 instanceof Set) && (c1.isEmpty()), where we save unnecessary O(c2.size()) iterations