code: protected boolean lookahead() {
          assert next == null : "looking ahead when next is already loaded";
          while(inner.hasNext()) {
              next = transform(inner.next());
              if(next!=null) {
                  return true;
              }
          }
          noteExhausted();
          return false;
      }
docs: /* (non-Javadoc)
  @see org.archive.util.iterator.LookaheadIterator#lookahead()