course institution fix

app/service/course/institution.js

@@ -34,7 +34,8 @@ class InstitutionService extends Service {
       let cat_ids = [ cat_id ];
       cat_ids = cat_ids.concat(R.pluck('id', next_cat)).concat(R.pluck('id', next_next_cat));
       const institutions = await ctx.classModel.CourseInstitutionToCat.all({ where: { cat_id: { $in: cat_ids } } });
-      where.id = { $in: R.pluck('institution_id', institutions) };
+      const institutions_ids = Array.from(new Set(R.pluck('institution_id', institutions)));
+      institutions_ids.length !== 0 ? where.id = { $in:  institutions_ids } : [];
     }
     if (Number(ages)) {
       where.max_age = { $gte: ages };