Description:
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If a session cookie is not set, a new session id will be created and all works fine. However, if for some reason the session cookie is set, but an empty string, session_start() throws a warning and custom session handlers are called with an empty session id. In addition, no session cookies are set.

Test script:
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The test script involves setting empty cookies and such. This is the user land workaround I am using for now. 

if(isset($_COOKIE[ini_get("session.name")]) && empty($_COOKIE[ini_get("session.name")])){
    // The cookie is empty. This is bad.
    unset($_COOKIE[ini_get("session.name")]);
}
session_start();


Expected result:
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An empty session cookie should be treated the same as an unset session cookie.

Actual result:
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Empty session cookies are treated as session ids, but warned and cause sessions to not be saved.