docs: public MetricName resolve(String p) {
          final String next;
  
          if (p != null && !p.isEmpty()) {
              if (key != null && !key.isEmpty()) {
                  next = key + SEPARATOR + p;
              } else {
                  next = p;
              }
          } else {
              next = this.key;
          }
  
          return new MetricName(next, tags);
      }