/**
   * Invoked when a {@code Future} computation fails or is canceled.
   *
   * <p>If the future's {@link Future#get() get} method throws an {@link ExecutionException}, then
   * the cause is passed to this method. Any other thrown object is passed unaltered.
   */
  void onFailure(Throwable t);

 * closing streams for you.
 *
 * <p>This package is a part of the open-source <a href="https://github.com/google/guava">Guava</a>
 * library. For more information on Sources and Sinks as well as other features of this package, see
 * <a href="https://github.com/google/guava/wiki/IOExplained">I/O Explained</a> on the Guava wiki.
 *
 * @author Chris Nokleberg
 */
@CheckReturnValue
@ParametersAreNonnullByDefault

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this software without specific prior written permission.

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First let's see how editors, mypy and other tools would see this.

`BaseUser` has the base fields. Then `UserIn` inherits from `BaseUser` and adds the `password` field, so, it will include all the fields from both models.

We annotate the function return type as `BaseUser`, but we are actually returning a `UserIn` instance.