diff --git a/src/mesh/node_group_inline_impl.hh b/src/mesh/node_group_inline_impl.hh
index c42d080dd..f7ff2a079 100644
--- a/src/mesh/node_group_inline_impl.hh
+++ b/src/mesh/node_group_inline_impl.hh
@@ -1,97 +1,100 @@
 /**
  * @file   node_group_inline_impl.hh
  *
  * @author Nicolas Richart <nicolas.richart@epfl.ch>
  *
  * @date creation: Fri Jun 18 2010
  * @date last modification: Sun Aug 13 2017
  *
  * @brief  Node group inline function definitions
  *
  *
  * Copyright (©)  2010-2018 EPFL (Ecole Polytechnique Fédérale de Lausanne)
  * Laboratory (LSMS - Laboratoire de Simulation en Mécanique des Solides)
  *
  * Akantu is free  software: you can redistribute it and/or  modify it under the
  * terms  of the  GNU Lesser  General Public  License as published by  the Free
  * Software Foundation, either version 3 of the License, or (at your option) any
  * later version.
  *
  * Akantu is  distributed in the  hope that it  will be useful, but  WITHOUT ANY
  * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  * A PARTICULAR PURPOSE. See  the GNU  Lesser General  Public License  for more
  * details.
  *
  * You should  have received  a copy  of the GNU  Lesser General  Public License
  * along with Akantu. If not, see <http://www.gnu.org/licenses/>.
  *
  */
 
 /* -------------------------------------------------------------------------- */
 
 namespace akantu {
 
 /* -------------------------------------------------------------------------- */
 inline NodeGroup::const_node_iterator NodeGroup::begin() const {
   return node_group.begin();
 }
 
 /* -------------------------------------------------------------------------- */
 inline NodeGroup::const_node_iterator NodeGroup::end() const {
   return node_group.end();
 }
 
 /* -------------------------------------------------------------------------- */
 inline NodeGroup::const_node_iterator NodeGroup::add(UInt node,
                                                      bool check_for_duplicate) {
   if (check_for_duplicate) {
     const_node_iterator it = std::find(begin(), end(), node);
     if (it == node_group.end()) {
       node_group.push_back(node);
       return (node_group.end() - 1);
     }
     return it;
   }
 
   node_group.push_back(node);
   return (node_group.end() - 1);
 }
 
 /* -------------------------------------------------------------------------- */
 inline void NodeGroup::remove(UInt node) {
   Array<UInt>::iterator<> it = this->node_group.begin();
   Array<UInt>::iterator<> end = this->node_group.end();
   AKANTU_DEBUG_ASSERT(it != end, "The node group is empty!!");
   for (; it != node_group.end(); ++it) {
     if (*it == node) {
       it = node_group.erase(it);
     }
   }
   AKANTU_DEBUG_ASSERT(it != end, "The node was not found!");
 }
 
+/* -------------------------------------------------------------------------- */
+inline bool NodeGroup::empty() const { return node_group.empty(); }
+
 /* -------------------------------------------------------------------------- */
 inline UInt NodeGroup::size() const { return node_group.size(); }
 
 /* -------------------------------------------------------------------------- */
 struct FilterFunctor;
 
 template <typename T> void NodeGroup::applyNodeFilter(T & filter) {
   AKANTU_DEBUG_IN();
 
   AKANTU_DEBUG_ASSERT(T::type == FilterFunctor::_node_filter_functor,
                       "NodeFilter can only apply node filter functor");
 
   Array<UInt>::iterator<> it = this->node_group.begin();
 
   for (; it != node_group.end(); ++it) {
     /// filter == true -> keep node
     if (!filter(*it)) {
       it = node_group.erase(it);
     }
   }
 
   AKANTU_DEBUG_OUT();
 }
 
 } // namespace akantu