code: @NotNull public static <T> Single<T> from(@NotNull final ApolloStoreOperation<T> operation) {
      checkNotNull(operation, "operation == null");
      return Single.create(new SingleOnSubscribe<T>() {
        @Override
        public void subscribe(final SingleEmitter<T> emitter) {
          operation.enqueue(new ApolloStoreOperation.Callback<T>() {
            @Override
            public void onSuccess(T result) {
              emitter.onSuccess(result);
            }
  
            @Override
            public void onFailure(Throwable t) {
              emitter.onError(t);
            }
          });
        }
      });
    }
docs: Converts an {@link ApolloStoreOperation} to a Single.
  
  @param operation the ApolloStoreOperation to convert
  @param <T>       the value type
  @return the converted Single