Suppress warning

src/storm/storage/jani/JSONExporter.cpp

@@ -525,6 +525,7 @@ namespace storm {
                 }
             }
             STORM_LOG_ASSERT(false, "Expression variable '" << expression.getVariableName() << "' not known in Jani data structures.");
+            return modernjson::json(); // should not reach this point.
         }
         boost::any ExpressionToJson::visit(storm::expressions::UnaryBooleanFunctionExpression const& expression, boost::any const& data) {
             modernjson::json opDecl;