diff --git a/src/core/wrapper/layout/flex/flex.horizontal.js b/src/core/wrapper/layout/flex/flex.horizontal.js
index daaaa2f3d..e91c02675 100644
--- a/src/core/wrapper/layout/flex/flex.horizontal.js
+++ b/src/core/wrapper/layout/flex/flex.horizontal.js
@@ -37,10 +37,10 @@ BI.FlexHorizontalLayout = BI.inherit(BI.Layout, {
     _addElement: function (i, item) {
         var o = this.options;
         var w = BI.FlexHorizontalLayout.superclass._addElement.apply(this, arguments);
-        var columnSize = o.columnSize.length > 0 ? o.columnSize[i] : item.width >= 1 ? "" : item.width;
+        var columnSize = o.columnSize.length > 0 ? o.columnSize[i] : item.width >= 1 ? null : item.width;
         if (o.columnSize.length > 0) {
             if (item.width >= 1 && o.columnSize[i] >= 1 && o.columnSize[i] !== item.width) {
-                columnSize = "";
+                columnSize = null;
             }
         }
         w.element.css({
diff --git a/src/core/wrapper/layout/flex/flex.vertical.js b/src/core/wrapper/layout/flex/flex.vertical.js
index 0ce9dc348..85c117c50 100644
--- a/src/core/wrapper/layout/flex/flex.vertical.js
+++ b/src/core/wrapper/layout/flex/flex.vertical.js
@@ -36,10 +36,10 @@ BI.FlexVerticalLayout = BI.inherit(BI.Layout, {
     _addElement: function (i, item) {
         var o = this.options;
         var w = BI.FlexVerticalLayout.superclass._addElement.apply(this, arguments);
-        var rowSize = o.rowSize.length > 0 ? o.rowSize[i] : item.height >= 1 ? "" : item.height;
+        var rowSize = o.rowSize.length > 0 ? o.rowSize[i] : item.height >= 1 ? null : item.height;
         if (o.rowSize.length > 0) {
             if (item.height >= 1 && o.rowSize[i] >= 1 && o.rowSize[i] !== item.height) {
-                rowSize = "";
+                rowSize = null;
             }
         }
         w.element.css({
diff --git a/src/core/wrapper/layout/flex/wrapper/flex.wrapper.horizontal.js b/src/core/wrapper/layout/flex/wrapper/flex.wrapper.horizontal.js
index 830af8501..4a23a9024 100644
--- a/src/core/wrapper/layout/flex/wrapper/flex.wrapper.horizontal.js
+++ b/src/core/wrapper/layout/flex/wrapper/flex.wrapper.horizontal.js
@@ -33,10 +33,10 @@ BI.FlexWrapperHorizontalLayout = BI.inherit(BI.Layout, {
     _addElement: function (i, item) {
         var o = this.options;
         var w = BI.FlexWrapperHorizontalLayout.superclass._addElement.apply(this, arguments);
-        var columnSize = o.columnSize.length > 0 ? o.columnSize[i] : item.width >= 1 ? "" : item.width;
+        var columnSize = o.columnSize.length > 0 ? o.columnSize[i] : item.width >= 1 ? null : item.width;
         if (o.columnSize.length > 0) {
             if (item.width >= 1 && o.columnSize[i] >= 1 && o.columnSize[i] !== item.width) {
-                columnSize = "";
+                columnSize = null;
             }
         }
         w.element.css({
diff --git a/src/core/wrapper/layout/flex/wrapper/flex.wrapper.vertical.js b/src/core/wrapper/layout/flex/wrapper/flex.wrapper.vertical.js
index f589ce929..62a38afbc 100644
--- a/src/core/wrapper/layout/flex/wrapper/flex.wrapper.vertical.js
+++ b/src/core/wrapper/layout/flex/wrapper/flex.wrapper.vertical.js
@@ -33,10 +33,10 @@ BI.FlexWrapperVerticalLayout = BI.inherit(BI.Layout, {
     _addElement: function (i, item) {
         var o = this.options;
         var w = BI.FlexWrapperVerticalLayout.superclass._addElement.apply(this, arguments);
-        var rowSize = o.rowSize.length > 0 ? o.rowSize[i] : item.height >= 1 ? "" : item.height;
+        var rowSize = o.rowSize.length > 0 ? o.rowSize[i] : item.height >= 1 ? null : item.height;
         if (o.rowSize.length > 0) {
             if (item.height >= 1 && o.rowSize[i] >= 1 && o.rowSize[i] !== item.height) {
-                rowSize = "";
+                rowSize = null;
             }
         }
         w.element.css({