Added method to handle file extension for non existing files

Author: Gabriel Galvao da Gama

app/code/Magento/Customer/Model/Metadata/Form/File.php

@@ -182,7 +182,7 @@ protected function _validateByRules($value)
     {
         $label = $value['name'];
         $rules = $this->getAttribute()->getValidationRules();
-        $extension = $this->fileProcessor->getStat($value['name'])['extension'];
+        $extension = $this->getFileExtension($value['name']);
         $fileExtensions = ArrayObjectSearch::getArrayElementByName(
             $rules,
             'file_extensions'
@@ -220,6 +220,20 @@ protected function _validateByRules($value)
         return [];
     }
 
+    /**
+     * Get file extension from the file if it exists, otherwise, get from filename.
+     *
+     * @param string $fileName
+     * @return string
+     */
+    private function getFileExtension(string $fileName): string
+    {
+        if ($this->fileProcessor->isExist($fileName)) {
+            return $this->fileProcessor->getStat($fileName)['extension'];
+        }
+        return pathinfo($fileName, PATHINFO_EXTENSION);
+    }
+
     /**
      * Helper function that checks if the file was uploaded.
      *