code: public Boolean getBoolean(int index, boolean strict) throws JsonException {
          JsonElement el = get(index);
          Boolean res = null;
          if (strict && !el.isBoolean()) {
              throw Util.typeMismatch(index, el, "boolean", true);
          }
          if (el.isBoolean()) {
              res = el.asBoolean();
          }
          if (el.isString()) {
              res = Util.toBoolean(el.asString());
          }
          if (res == null)
              throw Util.typeMismatch(index, el, "boolean", strict);
          return res;
      }
docs: Returns the value at {@code index} if it exists and is a boolean or can
  be coerced to a boolean.
  
  @throws JsonException if the value at {@code index} doesn't exist or
  cannot be coerced to a boolean.