code: func (cache *Cache) SetStorage(address crypto.Address, key binary.Word256, value binary.Word256) error {
  	if cache.readonly {
  		return errors.ErrorCodef(errors.ErrorCodeIllegalWrite,
  			"SetStorage called in a read-only context on account %v", address)
  	}
  	accInfo, err := cache.get(address)
  	if accInfo.account == nil {
  		return errors.ErrorCodef(errors.ErrorCodeIllegalWrite,
  			"SetStorage called on an account that does not exist: %v", address)
  	}
  	accInfo.Lock()
  	defer accInfo.Unlock()
  	if err != nil {
  		return err
  	}
  	if accInfo.removed {
  		return errors.ErrorCodef(errors.ErrorCodeIllegalWrite, "SetStorage on a removed account: %s", address)
  	}
  	accInfo.storage[key] = value
  	accInfo.updated = true
  	return nil
  }
docs: // NOTE: Set value to zero to remove.