diff --git a/common/include/Dict.hpp b/common/include/Dict.hpp
index fb005e7fae652778a711e349308df8dd5fd8b094..5d9f6545239eebba04b3929e0acd59524de95a68 100644
--- a/common/include/Dict.hpp
+++ b/common/include/Dict.hpp
@@ -30,10 +30,10 @@ class Dict
   private :
 
   void readFromFile(const char * filename);
+  void insert(const std::string & element);
 
   public :
 
-  void insert(const std::string & element);
   int getIndexOrInsert(const std::string & element);
   void setState(State state);
   State getState() const;
diff --git a/common/src/Dict.cpp b/common/src/Dict.cpp
index c451ecd15160d1358e43f6a1b23dbd9de3e0b31f..d96d954a8c89e415711791302630e95c81ca9c49 100644
--- a/common/src/Dict.cpp
+++ b/common/src/Dict.cpp
@@ -63,6 +63,9 @@ void Dict::insert(const std::string & element)
 
 int Dict::getIndexOrInsert(const std::string & element)
 {
+  if (element.empty())
+    return getIndexOrInsert(nullValueStr);
+
   const auto & found = elementsToIndexes.find(element);
 
   if (found == elementsToIndexes.end())