There are two unit tests SparseHLLTest#largeRangeSmokeTest() and FullHLLTest#largeRangeSmokeTest() that are supposed to test cardinalities of very large HLLs. However, if you insert
System.out.println(cardinality + ", " + expected);
 
at the bottom of them, you see that both the expected and actual cardinalities are 0. They should instead be a very large number.