code: func (c *HostCertParams) Check() error {
  	if c.HostID == "" && len(c.Principals) == 0 {
  		return trace.BadParameter("HostID [%q] or Principals [%q] are required",
  			c.HostID, c.Principals)
  	}
  	if c.ClusterName == "" {
  		return trace.BadParameter("ClusterName [%q] is required", c.ClusterName)
  	}
  
  	if err := c.Roles.Check(); err != nil {
  		return trace.Wrap(err)
  	}
  
  	return nil
  }
docs: // Check checks parameters for errors