import javax.annotation.CheckForNull;

/**
 * {@link Error} variant of {@link java.util.concurrent.ExecutionException}. As with {@code
 * ExecutionException}, the error's {@linkplain #getCause() cause} comes from a failed task,
 * possibly run in another thread. That cause should itself be an {@code Error}; if not, use {@code
 * ExecutionException} or {@link UncheckedExecutionException}. This allows the client code to