Add message when no parameters occur in final model

src/storm-pars/analysis/MonotonicityChecker.cpp

@@ -41,6 +41,9 @@ namespace storm {
                 }
 
                 std::map<carl::Variable, std::pair<bool, bool>> varsMonotone = analyseMonotonicity(i, lattice, matrix);
+                if (varsMonotone.size() == 0) {
+                    STORM_PRINT("Result is constant" << std::endl);
+                } else {
                     for (auto itr2 = varsMonotone.begin(); itr2 != varsMonotone.end(); ++itr2) {
                         if (itr2->second.first) {
                             STORM_PRINT("  - Monotone increasing in: " << itr2->first << std::endl);
@@ -53,8 +56,10 @@ namespace storm {
                             STORM_PRINT("  - Do not know if monotone decreasing in: " << itr2->first << std::endl);
                         }
                     }
-                result.insert(std::pair<storm::analysis::Lattice *, std::map<carl::Variable, std::pair<bool, bool>>>(
+                    result.insert(
+                            std::pair<storm::analysis::Lattice *, std::map<carl::Variable, std::pair<bool, bool>>>(
                                     lattice, varsMonotone));
+                }
                 ++i;
             }
             return result;