private static @NotNull MultiMap<VcsKey, VirtualFile> groupRootsByVcs(@NotNull Map<VirtualFile, VcsLogProvider> providers) {
    MultiMap<VcsKey, VirtualFile> result = MultiMap.create();
    for (Map.Entry<VirtualFile, VcsLogProvider> entry : providers.entrySet()) {
      VirtualFile root = entry.getKey();
      VcsKey vcs = entry.getValue().getSupportedVcs();
      result.putValue(vcs, root);
    }
    return result;
  }
private static @NotNull MultiMap<VcsKey, VirtualFile> groupRootsByVcs(@NotNull Map<VirtualFile, VcsLogProvider> providers)