diff --git a/src/main/java/org/nlpcn/es4sql/spatial/WktToGeoJsonConverter.java b/src/main/java/org/nlpcn/es4sql/spatial/WktToGeoJsonConverter.java
index d0267a44..48866d8b 100644
--- a/src/main/java/org/nlpcn/es4sql/spatial/WktToGeoJsonConverter.java
+++ b/src/main/java/org/nlpcn/es4sql/spatial/WktToGeoJsonConverter.java
@@ -1,4 +1,6 @@
 package org.nlpcn.es4sql.spatial;
+import org.elasticsearch.common.base.Joiner;
+
 import java.util.ArrayList;
 import java.util.List;
 
@@ -58,7 +60,7 @@ private static String multiLineStringCoordinatesFromWkt(String wkt) {
         for (int i=0;i<lineStrings.length;i++){
             coordinates[i] = lineStringCoordinatesFromWkt(lineStrings[i]);
         }
-        String multiLineStringCoordinates = String.join(",", coordinates);
+        String multiLineStringCoordinates = Joiner.on(',').join(coordinates);
         return String.format("[%s]", multiLineStringCoordinates);
 
     }
@@ -86,7 +88,7 @@ private static String multiPolygonCoordinatesFromWkt(String wkt) {
         for (int i=0;i<polygons.length;i++){
             polygonsCoordinates[i] = polygonCoordinatesFromWkt(polygons[i]);
         }
-        String coordinates = String.join(",", polygonsCoordinates);
+        String coordinates = Joiner.on(',').join(polygonsCoordinates);
         return String.format("[%s]", coordinates);
     }
 
@@ -109,7 +111,7 @@ private static String polygonCoordinatesFromWkt(String wkt) {
                 String polygonCoordinates = getJsonArrayFromListOfPoints(polygons[i]);
                 coordinatesOfPolygons[i] = polygonCoordinates;
             }
-            coordinates = String.join(",",coordinatesOfPolygons);
+            coordinates = Joiner.on(',').join(coordinatesOfPolygons);
         }
         else {
             coordinates = getJsonArrayFromListOfPoints(wkt);
@@ -123,7 +125,7 @@ private static String getJsonArrayFromListOfPoints(String pointsInWkt) {
         for(String point : points){
             coordinates.add(extractCoordinateFromPoint(point));
         }
-        String joinedCoordinates = String.join(",", coordinates);
+        String joinedCoordinates = Joiner.on(',').join(coordinates);
         return String.format("[%s]", joinedCoordinates);
     }