presto-main/src/main/java/io/prestosql/operator/aggregation/TypedSet.java/TypedSet/contains
class TypedSet:    public boolean contains(Block block, int position)
    {
        requireNonNull(block, "block must not be null");
        checkArgument(position >= 0, "position must be >= 0");

        if (block.isNull(position)) {
            return containsNullElement;
        }
        else {
            return blockPositionByHash.get(getHashPositionOfElement(block, position)) != EMPTY_SLOT;
        }
    }