return mixed if we failed detect castable type (#1306)

fixed #1305

tests/Console/ModelsCommand/LaravelCustomCasts/Casts/CastableWithoutReturnType.php

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Barryvdh\LaravelIdeHelper\Tests\Console\ModelsCommand\LaravelCustomCasts\Casts;
+
+use Illuminate\Contracts\Database\Eloquent\Castable;
+use Illuminate\Contracts\Database\Eloquent\CastsAttributes;
+
+class CastableWithoutReturnType implements Castable
+{
+    public static function castUsing(array $arguments)
+    {
+        return new class() implements CastsAttributes {
+            public function get($model, string $key, $value, array $attributes)
+            {
+                return new CastedProperty();
+            }
+
+            public function set($model, string $key, $value, array $attributes)
+            {
+                // TODO: Implement set() method.
+            }
+        };
+    }
+}