code: static Field fieldSerialPersistentFields(Class<?> cl) {
          try {
              Field f = cl.getDeclaredField("serialPersistentFields");
              int modifiers = f.getModifiers();
              if (Modifier.isStatic(modifiers) && Modifier.isPrivate(modifiers)
                      && Modifier.isFinal(modifiers)) {
                  if (f.getType() == ARRAY_OF_FIELDS) {
                      return f;
                  }
              }
          } catch (NoSuchFieldException nsm) {
              // Ignored
          }
          return null;
      }
docs: Return the java.lang.reflect.Field {@code serialPersistentFields}
  if class {@code cl} implements it. Return null otherwise.
  
  @param cl
  a java.lang.Class which to test
  @return {@code java.lang.reflect.Field} if the class has
  serialPersistentFields {@code null} if the class does not
  have serialPersistentFields