code: def get_subdomain_resolver(name, db_path=None, zonefiles_dir=None):
      
      opts = get_blockstack_opts()
      if not is_subdomains_enabled(opts):
          log.warn("Subdomain support is disabled")
          return None
  
      if db_path is None:
          db_path = opts['subdomaindb_path']
  
      if zonefiles_dir is None:
          zonefiles_dir = opts['zonefiles']
  
      db = SubdomainDB(db_path, zonefiles_dir)
      resolver_url = db.get_domain_resolver(name)
  
      return resolver_url
docs: Static method for determining the last-known resolver for a domain name.
      Returns the resolver URL on success
      Returns None on error