Retrieves a session ID from sessionStorage or generates a new one if it doesn't exist.
The session ID is a random string used to identify a unique user session.
Returns null|string
The session ID as a string, or null if window is undefined (e.g., during server-side rendering).
Retrieves a session ID from sessionStorage or generates a new one if it doesn't exist. The session ID is a random string used to identify a unique user session.