Oracle TDE - opening/closing an encryption wallet

I have a quick question relating to Oracle TDE. Could somebody please explain why both of the following pairs of commands appear to work when opening/closing an ecryption wallet? Is the wallet password actually needed for this or not? If not, when exactly do we need to use the password? Many thanks. administer key management set keystore close identified by ""; administer key management set keystore open identified by ""; administer key management set keystore close identified by "null"; administer key management set keystore open identified by "null";