* Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code
 *       ImmutableList.get} returns {@code E}, but that value is never {@code null}. (Accordingly,
 *       {@code ImmutableList} is declared to forbid {@code ImmutableList<@Nullable String>}.)

 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code
 *       ImmutableList.get} returns {@code E}, but that value is never {@code null}. (Accordingly,
 *       {@code ImmutableList} is declared to forbid {@code ImmutableList<@Nullable String>}.)

 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code
 *       ImmutableList.get} returns {@code E}, but that value is never {@code null}. (Accordingly,
 *       {@code ImmutableList} is declared to forbid {@code ImmutableList<@Nullable String>}.)

 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code
 *       ImmutableList.get} returns {@code E}, but that value is never {@code null}. (Accordingly,
 *       {@code ImmutableList} is declared to forbid {@code ImmutableList<@Nullable String>}.)

 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code
 *       ImmutableList.get} returns {@code E}, but that value is never {@code null}. (Accordingly,
 *       {@code ImmutableList} is declared to forbid {@code ImmutableList<@Nullable String>}.)

 * Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code
 *       ImmutableList.get} returns {@code E}, but that value is never {@code null}. (Accordingly,
 *       {@code ImmutableList} is declared to forbid {@code ImmutableList<@Nullable String>}.)

    /**
     * Invoked just before session is created with a mutable map that carries collected user properties so far.
     *
     * @param userProperties The mutable user properties, never {@code null}.
     */
    void contribute(Map<String, String> userProperties);

     * Builds the effective settings of the specified settings files.
     *
     * @param request The settings building request that holds the parameters, must not be {@code null}.
     * @return The result of the settings building, never {@code null}.
     * @throws SettingsBuildingException If the effective settings could not be built.
     */
    SettingsBuildingResult build(SettingsBuildingRequest request) throws SettingsBuildingException;

   *
   * <p>If the implementation of this method cannot correctly handle a particular code point then it
   * should either throw an appropriate runtime exception or return a suitable replacement
   * character. It must never silently discard invalid input as this may constitute a security risk.
   *
   * @param cp the Unicode code point to escape if necessary
   * @return the replacement characters, or {@code null} if no escaping was needed
   */

   */
  @Throws(IOException::class)
  fun trailers(): Headers = trailersFn()

  /**
   * Peeks up to [byteCount] bytes from the response body and returns them as a new response
   * body. If fewer than [byteCount] bytes are in the response body, the full response body is
   * returned. If more than [byteCount] bytes are in the response body, the returned value
   * will be truncated to [byteCount] bytes.
   *