code: func (a *ArgType) reniltype(typ string) string {
  	if strings.Contains(typ, ".") {
  		return typ
  	}
  
  	if strings.HasSuffix(typ, "{}") {
  		if _, ok := a.KnownTypeMap[typ[:len(typ)-2]]; ok {
  			return typ
  		}
  
  		pkg := a.CustomTypePackage
  		if pkg != "" {
  			pkg = pkg + "."
  		}
  
  		return pkg + typ
  	}
  
  	return typ
  }
docs: // reniltype checks typ against known nil types (similar to retype), prefixing
  // ArgType.CustomTypePackage (if applicable).