errors/registry.go
func (r *registry) Get(code Code) *ErrDescriptor {
	r.RLock()
	defer r.RUnlock()
	return r.byCode[code]
}
func (r *registry) Get(code Code) *ErrDescriptor {
	r.RLock()
	defer r.RUnlock()
	return r.byCode[code]
}
// Get returns the descriptor if it exists or nil otherwise