disappearing text in derived fields

using in ReportSmith a derived field in the dbase adress file with

rtrim(..familyName)+' '+..firstName

produces the correct full name if both (familyName and firstName) exist.
But why is the text missing if firstName is empty?

Many thanks for your help in advance

Ronny

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Dipl. Math+Inf ETH
Ronny Straus
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