diff --git a/.gitignore b/.gitignore
index 193239d..7c0b8ce 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,4 +4,5 @@ composer.lock
 composer.phar
 php-cs-fixer.phar
 
-vendor
+vendor/
+.idea/
diff --git a/DependencyInjection/ObHighchartsExtension.php b/DependencyInjection/ObHighchartsExtension.php
index dd9a505..b61b054 100644
--- a/DependencyInjection/ObHighchartsExtension.php
+++ b/DependencyInjection/ObHighchartsExtension.php
@@ -2,6 +2,7 @@
 
 namespace Ob\HighchartsBundle\DependencyInjection;
 
+use Exception;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\HttpKernel\DependencyInjection\Extension;
@@ -16,6 +17,8 @@ class ObHighchartsExtension extends Extension
 {
     /**
      * {@inheritDoc}
+     *
+     * @throws Exception
      */
     public function load(array $configs, ContainerBuilder $container)
     {
diff --git a/Highcharts/AbstractChart.php b/Highcharts/AbstractChart.php
index 71334d9..f400294 100644
--- a/Highcharts/AbstractChart.php
+++ b/Highcharts/AbstractChart.php
@@ -148,6 +148,8 @@ protected function renderEngine($engine)
         } elseif ($engine == 'jquery') {
             return "$(function () {";
         }
+
+        return '';
     }
 
     /**
diff --git a/Highcharts/ChartOption.php b/Highcharts/ChartOption.php
index f68be84..49046f7 100644
--- a/Highcharts/ChartOption.php
+++ b/Highcharts/ChartOption.php
@@ -2,6 +2,8 @@
 
 namespace Ob\HighchartsBundle\Highcharts;
 
+use stdClass;
+
 /**
  * This class is part of the Ob/HighchartsBundle
  * See Highcharts documentation at http://www.highcharts.com/ref/#chart
@@ -16,7 +18,7 @@ class ChartOption
     public function __construct($name)
     {
         $this->option_name = $name;
-        $this->{$name} = new \stdClass();
+        $this->{$name} = new stdClass();
     }
 
     /**
@@ -41,15 +43,14 @@ public function __call($name, $value)
     public function __get($name)
     {
         $option_name = $this->option_name;
-        $value = $this->{$option_name}->{$name};
 
-        return $value;
+        return $this->{$option_name}->{$name};
     }
 
     /**
      * @param string $name
      *
-     * @return mixed
+     * @return bool
      */
     public function __isset($name)
     {
diff --git a/Highcharts/Highchart.php b/Highcharts/Highchart.php
index f7b4b4f..e1fa39d 100644
--- a/Highcharts/Highchart.php
+++ b/Highcharts/Highchart.php
@@ -29,10 +29,9 @@ public function __construct()
      */
     public function render($engine = 'jquery')
     {
-        $chartJS = "";
-        $chartJS .= $this->renderEngine($engine);
+        $chartJS = $this->renderEngine($engine);
         $chartJS .= $this->renderOptions();
-        $chartJS .= "\n    var " . (isset($this->chart->renderTo) ? $this->chart->renderTo : 'chart') . " = new Highcharts.Chart({\n";
+        $chartJS .= "\n    var " . ($this->chart->renderTo ?? 'chart') . " = new Highcharts.Chart({\n";
 
         // Chart
         $chartJS .= $this->renderWithJavascriptCallback($this->chart->chart, "chart");
diff --git a/Highcharts/Highstock.php b/Highcharts/Highstock.php
index 90f1aa2..bf6d1ae 100644
--- a/Highcharts/Highstock.php
+++ b/Highcharts/Highstock.php
@@ -18,10 +18,9 @@ class Highstock extends AbstractChart implements ChartInterface
      */
     public function render($engine = 'jquery')
     {
-        $chartJS = "";
-        $chartJS .= $this->renderEngine($engine);
+        $chartJS = $this->renderEngine($engine);
         $chartJS .= $this->renderOptions();
-        $chartJS .= "\n    var " . (isset($this->chart->renderTo) ? $this->chart->renderTo : 'chart') . " = new Highcharts.StockChart({\n";
+        $chartJS .= "\n    var " . ($this->chart->renderTo ?? 'chart') . " = new Highcharts.StockChart({\n";
 
         // Chart Option
         $chartJS .= $this->renderWithJavascriptCallback($this->chart->chart, "chart");
diff --git a/composer.json b/composer.json
index 19e1b77..dca8e77 100644
--- a/composer.json
+++ b/composer.json
@@ -12,25 +12,27 @@
     ],
 
     "require": {
-        "php": "^7.2",
+        "php": "^7.2 || ^8.0",
+        "ext-json": "*",
         "symfony/http-kernel": "^4.4 || ^5.0",
         "symfony/dependency-injection": "^4.4 || ^5.0",
         "symfony/config": "^4.4 || ^5.0",
         "symfony/yaml": "^4.4 || ^5.0",
         "twig/twig": "^2.10 || ^3.0",
-        "laminas/laminas-json": "^3.1"
+        "laminas/laminas-json": "^3.3"
     },
     "require-dev": {
         "symfony/phpunit-bridge": "^4.4 || ^5.0",
         "symfony/framework-bundle": "^4.4 || ^5.0",
-        "nyholm/symfony-bundle-test": "^1.6.1"
+        "nyholm/symfony-bundle-test": "^1.6.1",
+        "phpcompatibility/php-compatibility": "^9.3"
     },
     "autoload": {
         "psr-4": { "Ob\\HighchartsBundle\\": "" }
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "1.8.x-dev"
+            "dev-master": "2.0.x-dev"
         }
     }
 }