code: public static AsciiString of(AsciiString name) {
          final AsciiString lowerCased = name.toLowerCase();
          final AsciiString cached = map.get(lowerCased);
          return cached != null ? cached : lowerCased;
      }
docs: Lower-cases and converts the specified header name into an {@link AsciiString}. If {@code "name"} is
  a known header name, this method will return a pre-instantiated {@link AsciiString} to reduce
  the allocation rate of {@link AsciiString}.