Returns the time the session was stopped, or <tt>null</tt> if the session is still active.
<p/>
A session may become stopped under a number of conditions:
<ul>
<li>If the user logs out of the system, their current session is terminated (released).</li>
<li>If the session expires</li>
<li>The application explicitly calls {@link #stop()}</li>
<li>If there is an internal system error and the session state can no longer accurately
reflect the user's behavior, such in the case of a system crash</li>
</ul>
<p/>
Once stopped, a session may no longer be used. It is locked from all further activity.
@return The time the session was stopped, or <tt>null</tt> if the session is still
active.
Returns the time the session was stopped, or <tt>null</tt> if the session is still active. <p/> A session may become stopped under a number of conditions: <ul> <li>If the user logs out of the system, their current session is terminated (released).</li> <li>If the session expires</li> <li>The application explicitly calls {@link #stop()}</li> <li>If there is an internal system error and the session state can no longer accurately reflect the user's behavior, such in the case of a system crash</li> </ul> <p/> Once stopped, a session may no longer be used. It is locked from all further activity.
@return The time the session was stopped, or <tt>null</tt> if the session is still active.