code: func (c *MutableTLSCreds) Clone() credentials.TransportCredentials {
  	c.Lock()
  	newCfg, err := NewMutableTLS(c.config.Clone())
  	if err != nil {
  		panic("validation error on Clone")
  	}
  	c.Unlock()
  	return newCfg
  }
docs: // Clone returns new MutableTLSCreds created from underlying *tls.Config.
  // It panics if validation of underlying config fails.