bug with if ... then ... clause in views

While trying to create some views I stumbled on some
problem with using the if-then clause. Here is a
simple example :

CREATE OR REPLACE VIEW public.SomeView
  as select d.id,
  if (true) then d.DocNumber endif from
public.Z_Documents as d;

I get the following error :
 syntax error at or near "then" at character 72

I don't have a clue what is going on here. Any
suggestions?

Thanks in advance,
Emil

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