fixed missing return statements

src/storm/settings/modules/EigenEquationSolverSettings.cpp

@@ -113,6 +113,7 @@ namespace storm {
                     case EigenEquationSolverSettings::LinearEquationMethod::DGMRES: out << "dgmres"; break;
                     case EigenEquationSolverSettings::LinearEquationMethod::SparseLU: out << "sparselu"; break;
                 }
+                return out;
             }
             
         } // namespace modules

src/storm/settings/modules/NativeEquationSolverSettings.cpp

@@ -120,6 +120,7 @@ namespace storm {
                     case NativeEquationSolverSettings::LinearEquationMethod::WalkerChae: out << "walkerchae"; break;
                     case NativeEquationSolverSettings::LinearEquationMethod::Power: out << "power"; break;
                 }
+                return out;
             }
             
         } // namespace modules