Removes (unbinds) the object bound to this session under the specified {@code key} name.
@param key the name uniquely identifying the object to remove
@return the object removed or {@code null} if there was no object bound under the name
{@code key}.
@throws InvalidSessionException if this session has stopped or expired prior to calling
this method.
Removes (unbinds) the object bound to this session under the specified {@code key} name.
@param key the name uniquely identifying the object to remove @return the object removed or {@code null} if there was no object bound under the name {@code key}. @throws InvalidSessionException if this session has stopped or expired prior to calling this method.