Data points transformation not showing values

I am following the instructions on the lesson:

https://learn.cognite.com/path/cognite-data-fusion-fundamentals/working-with-cdf-integrate/865148

SELECT 

concat('FirstnameBirthyear:',dp.sensor) AS externalId,

cast(time_stamp/1000 as timestamp) AS timestamp,

cast(value AS double)

FROM IFSDB.values AS dp,
 

--selecting from _cdf.timeseries means we select from the timeseries we ingested to CDF earlier. We do this to make sure all the time series we try to add data points to actually exist
 

_cdf.timeseries AS ts WHERE CONCAT('FirstnameBirthyear:',dp.sensor) = ts.externalId

I run the sql query modifying the FirstnameBirthyear values according with my name, but when I apply Preview, it doesn´t show any values. 

The result of the Preview query:

The query is syntactically correct, but returned 0 rows of data.

I was expecting to see some values as the other exercises. Is that a normal response on the lesson?