public @NotNull List<Pair<C,Collection<VirtualFile>>> createConfigurations(@NotNull Collection<? extends VirtualFile> files,
                                                                    @NotNull Collection<? extends C> existentFacetConfigurations) {
    final C configuration = createConfiguration(files);
    if (configuration != null) {
      return Collections.singletonList(Pair.create(configuration, (Collection<VirtualFile>)files));
    }
    return Collections.emptyList();
  }
public @NotNull List<Pair<C,Collection<VirtualFile>>> createConfigurations(@NotNull Collection<? extends VirtualFile> files,
                                                                    @NotNull Collection<? extends C> existentFacetConfigurations)