Fix facade::$app could be nullable

src/Facade/Pdf.php

@@ -4,6 +4,7 @@
 
 use Barryvdh\DomPDF\PDF as BasePDF;
 use Illuminate\Support\Facades\Facade as IlluminateFacade;
+use RuntimeException;
 
 /**
  * @method static BasePDF setBaseHost(string $baseHost)
@@ -43,14 +44,32 @@ protected static function getFacadeAccessor()
     }
 
     /**
-     * Resolve a new instance
+     * Get the application instance behind the facade.
+     *
+     * @return \Illuminate\Contracts\Foundation\Application|null
+     */
+    public static function getFacadeApplication()
+    {
+        return static::$app;
+    }
+
+    /**
+     * Handle dynamic, static calls to the object.
+     *
      * @param string $method
      * @param array<mixed> $args
      * @return mixed
+     *
+     * @throws \RuntimeException
      */
     public static function __callStatic($method, $args)
     {
-        $instance = static::$app->make(static::getFacadeAccessor());
+        $app = static::getFacadeApplication();
+        if (! $app) {
+            throw new RuntimeException('Facade application has not been set.');
+        }
+
+        $instance = $app->make(static::getFacadeAccessor());
 
         return $instance->$method(...$args);
     }