missing text in derived fields in report smith

I'm using a dbase adress file with the odbc driver in ReportSmith.
I've defined a derived field fullname with
{fn ltrim( {fn RTRIM("ADR"."FIRSTNAME")} + ' ' + "ADR"."NAME")}

The result is that the resulting string is empty in the case either
name or firstname is missing.

WHY ?

Thanks in advance for your help

Ronny

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Dipl. Math+Inf ETH
Ronny Straus
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