code: public static void set100ContinueExpected(HttpMessage message, boolean expected) {
          if (expected) {
              message.headers().set(HttpHeaderNames.EXPECT, HttpHeaderValues.CONTINUE);
          } else {
              message.headers().remove(HttpHeaderNames.EXPECT);
          }
      }
docs: Sets or removes the {@code "Expect: 100-continue"} header to / from the
  specified message. If {@code expected} is {@code true},
  the {@code "Expect: 100-continue"} header is set and all other previous
  {@code "Expect"} headers are removed.  Otherwise, all {@code "Expect"}
  headers are removed completely.