<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def open_stored_file(value, url):
 """ Deserialize value for a given upload url and return open file. Returns None if deserialization fails. """

    upload = None
    result = deserialize_upload(value, url)
    filename = result['name']
    storage_class = result['storage']
    if storage_class and filename:
        storage = storage_class()
        if storage.exists(filename):
            upload = storage.open(filename)
            upload.name = os.path.basename(filename)
    return upload