code: func UpdateCluster(tx Tx, c *api.Cluster) error {
  	// Ensure the name is either not in use or already used by this same Cluster.
  	if existing := tx.lookup(tableCluster, indexName, strings.ToLower(c.Spec.Annotations.Name)); existing != nil {
  		if existing.GetID() != c.ID {
  			return ErrNameConflict
  		}
  	}
  
  	return tx.update(tableCluster, c)
  }
docs: // UpdateCluster updates an existing cluster in the store.
  // Returns ErrNotExist if the cluster doesn't exist.