@Override
 public void setRequestProperty(String name, String value) {
   Assertions.checkNotNull(name);
   Assertions.checkNotNull(value);
   synchronized (requestProperties) {
     requestProperties.put(name, value);
   }
 }
 @Override
 public void clearRequestProperty(String name) {
   Assertions.checkNotNull(name);
   synchronized (requestProperties) {
     requestProperties.remove(name);
   }
 }