diff --git a/index.js b/index.js
index 6a3bb701..8844a9bb 100644
--- a/index.js
+++ b/index.js
@@ -8,8 +8,9 @@ exports.collection = Interface.collection;
 exports.ensureAuthenticated = Interface.ensureAuthenticated;
 exports.StatSerializer = Interface.StatSerializer;
 exports.ResourceSerializer = Interface.ResourceSerializer;
+exports.Schemas = Interface.Schemas;
 
-exports.init = function(opts) {
+exports.init = function (opts) {
   exports.opts = opts;
 
   exports.getLianaName = function () {
@@ -38,13 +39,13 @@ exports.init = function(opts) {
 
   exports.ResourcesGetter = require('./services/resources-getter');
   exports.ResourceGetter = require('./services/resource-getter');
-  exports.ResourceCreator = require('./services/resource-creator');
-  exports.ResourceUpdater = require('./services/resource-updater');
-  exports.ResourceRemover = require('./services/resource-remover');
+  exports.ResourceCreator = opts.ResourceCreator || require('./services/resource-creator');
+  exports.ResourceUpdater = opts.ResourceUpdater || require('./services/resource-updater');
+  exports.ResourceRemover = opts.ResourceRemover || require('./services/resource-remover');
 
   exports.HasManyGetter = require('./services/has-many-getter');
-  exports.HasManyAssociator = require('./services/has-many-associator');
-  exports.HasManyDissociator = require('./services/has-many-dissociator');
+  exports.HasManyAssociator = opts.HasManyAssociator || require('./services/has-many-associator');
+  exports.HasManyDissociator = opts.HasManyDissociator || require('./services/has-many-dissociator');
   exports.BelongsToUpdater = require('./services/belongs-to-updater');
 
   exports.ValueStatGetter = require('./services/value-stat-getter');
@@ -92,13 +93,13 @@ exports.init = function(opts) {
       return new P(function (resolve, reject) {
         if (customerId) {
           return userModel
-          .findById(customerId)
-          .lean()
-          .exec(function (err, customer) {
-            if (err) { return reject(err); }
-            if (!customer) { return reject(); }
-            resolve(customer);
-          });
+            .findById(customerId)
+            .lean()
+            .exec(function (err, customer) {
+              if (err) { return reject(err); }
+              if (!customer) { return reject(); }
+              resolve(customer);
+            });
         } else {
           resolve();
         }
diff --git a/package.json b/package.json
index 39241cbf..d39bb14a 100644
--- a/package.json
+++ b/package.json
@@ -23,7 +23,7 @@
   "dependencies": {
     "bluebird": "2.9.25",
     "flat": "1.6.0",
-    "forest-express": "1.1.10",
+    "forest-express": "kevin-frugier/forest-express#spk-1.1.10",
     "http-errors": "1.6.1",
     "lodash": "3.9.3",
     "moment": "2.10.6"
diff --git a/services/line-stat-getter.js b/services/line-stat-getter.js
index 4e27b185..4cb56aa5 100644
--- a/services/line-stat-getter.js
+++ b/services/line-stat-getter.js
@@ -193,7 +193,7 @@ function LineStatFinder(model, params, opts) {
         query = query.match(q);
       }
 
-      if (groupBy) {
+      if (!_.isEmpty(groupBy)) {
         var group = {
           _id: groupBy,
           count: { $sum: sum }
@@ -206,8 +206,11 @@ function LineStatFinder(model, params, opts) {
         query = query.group(group);
       }
 
-      query.sort(sort)
-        .project({
+      if (!_.isEmpty(sort)) {
+        query = query.sort(sort);
+      }
+
+      query.project({
           values: {
             key: '$_id.'+  params['group_by_field'],
             value: '$count'
diff --git a/services/pie-stat-getter.js b/services/pie-stat-getter.js
index 24771c8d..8a4d68a0 100644
--- a/services/pie-stat-getter.js
+++ b/services/pie-stat-getter.js
@@ -32,6 +32,10 @@ function PieStatGetter(model, params, opts) {
   }
 
   this.perform = function () {
+    if (!params['group_by_field']) {
+      return P.reject(new Error('Missing param `group_by_field`'));
+    }
+
     var populateGroupByField = getReference(params['group_by_field']);
 
     return new P(function (resolve, reject) {