Fix pool variable checking in query method

Author: Enes SAHIN

README.md

@@ -2,7 +2,7 @@
 # fluent-mysql
 
 
-![Image of version](https://img.shields.io/badge/npm-v1.2.0-blue)
+![Image of version](https://img.shields.io/badge/npm-v1.2.1-blue)
 ![Image of version](https://img.shields.io/badge/licence-MIT-yellowgreen)
 
 **fluent-mysql** is a query builder for MySQL. It performs basic database operations using [mysql](https://www.npmjs.com/package/mysql) library.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "fluent-mysql",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "description": "MySQL query builder to perform database operations",
   "main": "./lib/index.js",
   "dependencies": {

src/index.js

@@ -524,7 +524,7 @@ class Database {
    */
   query = queryStatement => {
     let self = this;
-    let connection = this.pool !== undefined ? this.pool : this.connection;
+    let connection = this.pool !== null ? this.pool : this.connection;
     return new Promise( (resolve, reject) => {
       connection.query(queryStatement, function (error, results, fields) {
         if (error) reject( error );