fix(populate): skip checking refPath if the path to populate is und…

…efined

Fix #9340

lib/helpers/populate/getModelsMapForPopulate.js

@@ -282,7 +282,12 @@ module.exports = function getModelsMapForPopulate(model, docs, options) {
           originalModel :
           modelName[modelSymbol] ? modelName : connection.model(modelName);
       } catch (error) {
-        return error;
+        // If `ret` is undefined, we'll add an empty entry to modelsMap. We shouldn't
+        // execute a query, but it is necessary to make sure `justOne` gets handled
+        // correctly for setting an empty array (see gh-8455)
+        if (ret !== undefined) {
+          return error;
+        }
       }
 
       let ids = ret;