code: func (self *StateDB) StorageTrie(addr common.Address) Trie {
  	stateObject := self.getStateObject(addr)
  	if stateObject == nil {
  		return nil
  	}
  	cpy := stateObject.deepCopy(self)
  	return cpy.updateTrie(self.db)
  }
docs: // StorageTrie returns the storage trie of an account.
  // The return value is a copy and is nil for non-existent accounts.