isNullRTuple ::
       RTuple 
    -> Bool    
isNullRTuple t = 
    let -- if t is really Null, then the following must return an empty RTuple (since a Null RTuple has all its values equal with Null)
        checkt = HM.filter (\v -> isNotNull  v) t  --v /= Null) t 
    in if isRTupEmpty checkt 
            then True
            else False
isNullRTuple ::
       RTuple 
    -> Bool
isNullRTuple t = 
    let -- if t is really Null, then the following must return an empty RTuple (since a Null RTuple has all its values equal with Null)
        checkt = HM.filter (\v -> isNotNull  v) t  --v /= Null) t 
    in if isRTupEmpty checkt 
            then True
            else False
isNullRTuple t = 
    let -- if t is really Null, then the following must return an empty RTuple (since a Null RTuple has all its values equal with Null)
        checkt = HM.filter (\v -> isNotNull  v) t  --v /= Null) t 
    in if isRTupEmpty checkt 
            then True
            else False