Fix IndexSet::is_ascending_and_one_to_one for empty objects

diff --git a/source/base/index_set.cc b/source/base/index_set.cc
index 9b833fcb7c9c37a4357bb3ee18b637388d7e0127..8815d6919b5c9f30d246da8cadc98da5c82ffe4d 100644 (file)
--- a/source/base/index_set.cc
+++ b/source/base/index_set.cc
@@ -672,6 +672,9 @@ IndexSet::is_ascending_and_one_to_one(const MPI_Comm &communicator) const
   if (n_global_elements != size())
     return false;
 
+  if (n_global_elements == 0)
+    return true;
+
 #ifdef DEAL_II_WITH_MPI
   // Non-contiguous IndexSets can't be linear.
   const bool all_contiguous =