code: public B preflightResponseHeader(CharSequence name, Iterable<?> values) {
          requireNonNull(name, "name");
          requireNonNull(values, "values");
          checkArgument(!Iterables.isEmpty(values), "values should not be empty.");
          final ImmutableList.Builder builder = new Builder();
          int i = 0;
          for (Object value : values) {
              if (value == null) {
                  throw new NullPointerException("value[" + i + ']');
              }
              builder.add(value);
              i++;
          }
          preflightResponseHeaders.put(HttpHeaderNames.of(name), new ConstantValueSupplier(builder.build()));
          return self();
      }
docs: Specifies HTTP response headers that should be added to a CORS preflight response.
  
  <p>An intermediary like a load balancer might require that a CORS preflight request
  have certain headers set. This enables such headers to be added.
  
  @param name the name of the HTTP header.
  @param values the values for the HTTP header.
  @return {@code this} to support method chaining.