fixed case where no location variables were provided

src/storm-conv/settings/modules/JaniExportSettings.cpp

@@ -39,16 +39,18 @@ namespace storm {
             }
 
             std::vector<std::pair<std::string, std::string>> JaniExportSettings::getLocationVariables() const {
+                std::vector<std::pair<std::string, std::string>> result;
+                if (isLocationVariablesSet()) {
                     std::string argument = this->getOption(locationVariablesOptionName).getArgumentByName("variables").getValueAsString();
                     std::vector<std::string> arguments;
                     boost::split( arguments, argument, boost::is_any_of(","));
-                std::vector<std::pair<std::string, std::string>> result;
                     for (auto const& pair : arguments) {
                         std::vector<std::string> keyvaluepair;
                         boost::split( keyvaluepair, pair, boost::is_any_of("."));
                         STORM_LOG_THROW(keyvaluepair.size() == 2, storm::exceptions::IllegalArgumentException, "Expected a name of the form AUTOMATON.VARIABLE (with no further dots) but got " << pair);
                         result.emplace_back(keyvaluepair.at(0), keyvaluepair.at(1));
                     }
+                }
                 return result;
             }