*
     * @return true if previous page exists, false otherwise
     */
    public boolean isExistPrePage() {
        return existPrePage;
    }

    /**
     * Sets the flag indicating if a previous page exists.
     *
     * @param existPrePage true if previous page exists, false otherwise
     */
    public void setExistPrePage(final boolean existPrePage) {

      for any such Derivative Works as a whole, provided Your use,
      reproduction, and distribution of the Work otherwise complies with
      the conditions stated in this License.

   5. Submission of Contributions. Unless You explicitly state otherwise,
      any Contribution intentionally submitted for inclusion in the Work
      by You to the Licensor shall be under the terms and conditions of

      for any such Derivative Works as a whole, provided Your use,
      reproduction, and distribution of the Work otherwise complies with
      the conditions stated in this License.

   5. Submission of Contributions. Unless You explicitly state otherwise,
      any Contribution intentionally submitted for inclusion in the Work
      by You to the Licensor shall be under the terms and conditions of

     */
    Class<?> getElementClassOfCollection(int index);

    /**
     * Returns the key type if the parameter type of the method is a parameterized {@link Map}.
     *
     * @param index
     *            The index of the parameter
     * @return The key type if the parameter type is a parameterized {@link Map}, otherwise {@literal null}
     */

   * Returns the string if it is not null, or an empty string otherwise.
   *
   * @param string the string to test and possibly return
   * @return {@code string} if it is not null; {@code ""} otherwise
   */
  static String nullToEmpty(@Nullable String string) {
    return (string == null) ? "" : string;
  }

  /**
   * Returns the string if it is not empty, or a null string otherwise.
   *

     *
     * @return true if there is a previous page, false otherwise
     */
    public boolean isExistPrePage() {
        return existPrePage;
    }

    /**
     * Sets whether there is a previous page available.
     *
     * @param existPrePage true if there is a previous page, false otherwise
     */
    public void setExistPrePage(final boolean existPrePage) {

     * @param key the parameter key to look up
     * @return the parameter value if found, null otherwise
     */
    public Object get(final String key) {
        return params.get(key);
    }

    /**
     * Retrieves a parameter value as a String.
     * If the stored value is already a String, it is returned directly.
     * Otherwise, the toString() method is called on the value.
     *
     * @param key the parameter key to look up

    return new Present<>(checkNotNull(reference));
  }

  /**
   * If {@code nullableReference} is non-null, returns an {@code Optional} instance containing that
   * reference; otherwise returns {@link Optional#absent}.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
   * {@code Optional.ofNullable}.
   */

    /**
     * Checks if a previous page exists.
     * @return true if a previous page exists, false otherwise.
     */
    public boolean isExistPrePage() {
        return existPrePage;
    }

    /**
     * Sets whether a previous page exists.
     * @param existPrePage true if a previous page exists, false otherwise.
     */
    public void setExistPrePage(final boolean existPrePage) {

     * @return True if the user's information is editable, false otherwise.
     */
    default boolean isEditable() {
        return false;
    }

    /**
     * Refreshes the user's information from the underlying data source.
     * @return True if refresh was successful, false otherwise.
     */
    default boolean refresh() {
        return false;
    }