prevent creation of empty arrays of includes

lib/dao-factory.js

@@ -1593,6 +1593,7 @@ module.exports = (function() {
         // run recursively if nested
         if (nested) {
           addAllIncludes(model, thisInclude.include)
+          if (thisInclude.include.length == 0) delete thisInclude.include
         }
       })
       used.pop()