Oct 18 (Reuters) - Walmart Inc-backed robotics and automation company Symbotic is in talks to merge with a blank-check vehicle backed by SoftBank Group Corp in a deal that would value the combined firm at $4.5 billion, Sky News reported here on Monday. Walmart and Symbotic did not immediately respond to Reuters requests for comment. (Reporting by Niket Nishant in Bengaluru) Our Standards: The Thomson Reuters Trust Principles.