code: @CheckReturnValue
      @SchedulerSupport(SchedulerSupport.NONE)
      public final Single<Boolean> contains(final Object value, final BiPredicate<Object, Object> comparer) {
          ObjectHelper.requireNonNull(value, "value is null");
          ObjectHelper.requireNonNull(comparer, "comparer is null");
          return RxJavaPlugins.onAssembly(new SingleContains<T>(this, value, comparer));
      }
docs: Signals true if the current Single signals a success value that is equal with
  the value provided by calling a bi-predicate.
  <dl>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code contains} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  @param value the value to compare against the success value of this Single
  @param comparer the function that receives the success value of this Single, the value provided
  and should return true if they are considered equal
  @return the new Single instance
  @since 2.0