From 774fffe698cb09c2389f37e721edbc674b7cb824 Mon Sep 17 00:00:00 2001
From: Martin Kronbichler <martin.kronbichler@uni-a.de>
Date: Mon, 26 Sep 2022 11:53:35 +0200
Subject: [PATCH] Add shortcut to detection of whether a DoF is constrained

---
 include/deal.II/lac/affine_constraints.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/deal.II/lac/affine_constraints.h b/include/deal.II/lac/affine_constraints.h
index 2912e4457b..0fa3fafc51 100644
--- a/include/deal.II/lac/affine_constraints.h
+++ b/include/deal.II/lac/affine_constraints.h
@@ -2196,6 +2196,9 @@ template <typename number>
 inline bool
 AffineConstraints<number>::is_constrained(const size_type index) const
 {
+  if (lines.empty())
+    return false;
+
   const size_type line_index = calculate_line_index(index);
   return ((line_index < lines_cache.size()) &&
           (lines_cache[line_index] != numbers::invalid_size_type));
@@ -2223,6 +2226,9 @@ template <typename number>
 inline const std::vector<std::pair<types::global_dof_index, number>> *
 AffineConstraints<number>::get_constraint_entries(const size_type line_n) const
 {
+  if (lines.empty())
+    return nullptr;
+
   // check whether the entry is constrained. could use is_constrained, but
   // that means computing the line index twice
   const size_type line_index = calculate_line_index(line_n);
-- 
2.39.5