Config::print now print '_' symbol instead of blank

reading_machine/src/Config.cpp

@@ -71,8 +71,12 @@ void Config::print(FILE * dest) const
     }
     for (unsigned int i = 0; i < getNbColumns()-1; i++)
     {
-      auto & colContent = isPredicted(getColName(i)) ? getLastNotEmptyHypConst(i, getFirstLineIndex()+line) : getLastNotEmptyConst(i, line);
-      fmt::print(dest, "{}{}", colContent, i < getNbColumns()-2 ? "\t" : "\n");
+      auto & colContent = isPredicted(getColName(i)) ? getLastNotEmptyHypConst(i, getFirstLineIndex()+line) : getLastNotEmptyConst(i, getFirstLineIndex()+line);
+      std::string valueToPrint = colContent;
+      if (valueToPrint.empty())
+        valueToPrint = "_";
+
+      fmt::print(dest, "{}{}", valueToPrint, i < getNbColumns()-2 ? "\t" : "\n");
     }
     if (getLastNotEmptyConst(EOSColName, getFirstLineIndex()+line) == EOSSymbol1)
       fmt::print(dest, "\n");