private static @NotNull Map<VirtualFile, VcsLogProvider.Requirements> prepareRequirements(@NotNull Collection<? extends VirtualFile> roots,
                                                                                              int commitCount,
                                                                                              @Nullable Map<VirtualFile, CompressedRefs> prevRefs) {
      Map<VirtualFile, VcsLogProvider.Requirements> requirements = new HashMap<>();
      for (VirtualFile root : roots) {
        requirements.put(root, prevRefs == null
                               ? new RequirementsImpl(commitCount, true, Collections.emptyList(), false)
                               : new RequirementsImpl(commitCount, true, prevRefs.get(root).getRefs()));
      }
      return requirements;
    }
private static @NotNull Map<VirtualFile, VcsLogProvider.Requirements> prepareRequirements(@NotNull Collection<? extends VirtualFile> roots,
                                                                                              int commitCount,
                                                                                              @Nullable Map<VirtualFile, CompressedRefs> prevRefs)