fix for the ajax error when removing an image/ clean up on empty log function

src/Plugin/Field/FieldFormatter/BgImgFieldFormatter.php

@@ -138,6 +138,9 @@ class BgImgFieldFormatter extends ResponsiveImageFormatter implements ContainerF
     // Load the files to render.
     $files = [];
     foreach ($items->getValue() as $item) {
+      if (!isset($file['file'])) {
+        continue;
+      }
       $files[] = [
         'file' => File::load($item['target_id']),
         'item' => $item
@@ -289,15 +292,4 @@ class BgImgFieldFormatter extends ResponsiveImageFormatter implements ContainerF
 
     return $css;
   }
-
-  /**
-   * Implement abstract method
-   *
-   * @param $level
-   * @param $message
-   * @param array $context
-   */
-  public function log($level, $message, array $context = []) {
-
-  }
 }