code: private static ByteBuffer max(ByteBuffer b1, ByteBuffer b2, AbstractType<?> comparator)
      {
          if (b1 == null)
              return b2;
          if (b2 == null)
              return b1;
  
          if (comparator.compare(b1, b2) >= 0)
              return b1;
          return b2;
      }
docs: return the max column
  
  note that comparator should not be of CompositeType!
  
  @param b1 lhs
  @param b2 rhs
  @param comparator the comparator to use
  @return the biggest column according to comparator