[6.x] Fix TypeError when asset last_modified meta is null (#14530)

Co-authored-by: Jason Varga <jason@pixelfear.com>

Author: v-Woody

src/Assets/Asset.php

@@ -601,7 +601,7 @@ public function mimeType()
      */
     public function lastModified()
     {
-        return Carbon::createFromTimestamp($this->meta('last_modified'), config('app.timezone'));
+        return Carbon::createFromTimestamp($this->meta('last_modified') ?? 0, config('app.timezone'));
     }
 
     /**

tests/Assets/AssetTest.php

@@ -663,6 +663,22 @@ public function it_gets_last_modified_time()
         $this->assertEquals(Carbon::parse('2017-01-02 14:35:00')->timestamp, $lastModified->timestamp);
     }
 
+    #[Test]
+    public function it_does_not_throw_when_getting_last_modified_and_file_doesnt_exist()
+    {
+        // This is really a workaround for an underlying bug.
+        // It's odd for an asset to not have a corresponding file.
+        // Once resolved, this test could be removed, although it doesn't hurt by being here.
+
+        Storage::fake('test');
+        // Intentionally do no not create the actual file.
+
+        $asset = (new Asset)->container($this->container)->path('foo/test.txt');
+
+        $lastModified = $asset->lastModified();
+        $this->assertInstanceOf(Carbon::class, $lastModified);
+    }
+
     #[Test]
     public function it_generates_and_clears_meta_caches()
     {