nvlRTuple ::
        ColumnName  -- ^ ColumnName key
    ->  RDataType   -- ^ Default value in the case of Null column values
    ->  RTuple      -- ^ input RTuple    
    ->  RTuple      -- ^ output RTuple
nvlRTuple c defaultVal tup  = 
    if isRTupEmpty tup
       then emptyRTuple
       else HM.map (\v -> nvl v defaultVal) tup
nvlRTuple ::
        ColumnName  -- ^ ColumnName key
    ->  RDataType   -- ^ Default value in the case of Null column values
    ->  RTuple      -- ^ input RTuple    
    ->  RTuple
nvlRTuple c defaultVal tup  = 
    if isRTupEmpty tup
       then emptyRTuple
       else HM.map (\v -> nvl v defaultVal) tup
nvlRTuple c defaultVal tup  = 
    if isRTupEmpty tup
       then emptyRTuple
       else HM.map (\v -> nvl v defaultVal) tup