code: public synchronized void set(int i, String k, String v) {
          grow();
          if (i < 0) {
              return;
          } else if (i >= nkeys) {
              add(k, v);
          } else {
              keys[i] = k;
              values[i] = v;
          }
      }
docs: Overwrite the previous key/val pair at location 'i'
  with the new k/v.  If the index didn't exist before
  the key/val is simply tacked onto the end.