def reset(secret_key=None):<EOL>
_thread_local_storage.secret_key = secret_key<EOL>
Reset the session.

By default, this resets the value of the secret to None so that, if
there was an earlier sanitation process ran on the same thread, then
a next call that needs the secret key of the session will generate a
new value for it.

This may also be used to set a predefined value for the secret key.

:param secret_key:
  Value to set as the new session secret key or None if a new one
  should be generated as soon as one is needed.