Check for plain objects

lib/model.js

@@ -1622,7 +1622,7 @@ module.exports = (function() {
     // otherwise this code will never run on includes of a already conditionable where
     if (options.include && options.include.length) {
       options.include.forEach(function(include) {
-        if (Utils._.isObject(include) && include.model) {
+        if (Utils._.isPlainObject(include) && include.model) {
           paranoidClause.call(include.model, include);
         }
       });