@Override
    public SharedConnectionDefinition remove(String key) {

        // There are no null share keys
        if (key == null)
            return null;

        // Attempt to retrieve only if non-null
        SharedConnectionDefinition definition = connectionMap.remove(key);
        if (definition == null)
            return null;

        // Close all associated tunnels and disallow further sharing
        definition.invalidate();
        return definition;

    }
Keeps track of the share key to SharedConnectionDefinition mapping.
extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/apache/guacamole/auth/jdbc/sharing/HashSharedConnectionMap.java