CreatedRelative not included in output when querying from CLI

Hi,

In a query like this:

wget --post-data 'user=<username>&pass=<pass>'  
'https://my.rt.server/REST/1.0/search/ticket?query=
Queue="My Queue" AND (Status = "open" OR Status = "new" OR Status = "Stalled")
&fields=id,Subject,Requestors,Owner,Status,Created,CreatedRelative
&orderby=-Created'

all requested fields are in the output, except CreatedRelative.
Why is that? Am I doing something wrong?

Thanks a lot in advance.
Cheers,
Jose