code: private int find(int key, int hash) {
          int index = index(hash);
          final int maxTry = capacity;
          for (int i = 0; i < maxTry; i++) {
              Object slot = values[index];
              if (slot == null) return -1;
              if (slot != GUARD) return keys[index] == key ? index : -1;
              index = nextIndex(index);
          }
          return -1;
      }
docs: Finds the slot of an existing value for `key`;