code: public static AsciiString of(CharSequence name) {
          if (name instanceof AsciiString) {
              return of((AsciiString) name);
          }
  
          final String lowerCased = Ascii.toLowerCase(requireNonNull(name, "name"));
          final AsciiString cached = map.get(lowerCased);
          return cached != null ? cached : AsciiString.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}.