must doesn't seem to be supported in deviation

[ankitjain093]

the following example of a deviation statement to add a must constraint to a leaf doesn't seem to be supported:

deviation /l2:l2vpn-svc/l2:sites/l2:site/l2:site-network-accesses/l2:site-network-access/l2:connection/l2:lag-interfaces/l2:lag-interface/l2:lacp/l2:mini-link-num {
        deviate add {
            must "count(../member-links/member-link) >= ." {
                error-message "Minimum links can't be less than configured member links";
            }
        }
    }