Bump min php Version to 7.4, fix PHPstan issues

Signed-off-by: Lukas Kämmerling <[email protected]>

Author: LKaemmerling

composer.json

@@ -15,7 +15,7 @@
         "lkaemmerling/prometheus_client_php": "*"
     },
     "require": {
-        "php": "^7.2|^8.0",
+        "php": "^7.4|^8.0",
         "ext-json": "*"
     },
     "require-dev": {

src/Prometheus/Exception/MetricJsonException.php

@@ -9,10 +9,14 @@
  */
 class MetricJsonException extends Exception
 {
+    private ?string $metricName;
 
-    private $metricName;
-    public function __construct($message = "", $code = 0, Exception $previous = null, ?string $metricName = null)
-    {
+    public function __construct(
+        string $message = "",
+        int $code = 0,
+        ?Exception $previous = null,
+        ?string $metricName = null
+    ) {
         parent::__construct($message, $code, $previous);
         $this->metricName = $metricName;
     }