dbpedia - SPARQL replace empty attributes with others -

i made sparql query using official dbpedia endpoint.

i'll take example main question:

select  ?museum ?englishabstract   ?russianabstract  {   ?museum dbpedia-owl:abstract ?englishabstract.  ?museum dbpedia-owl:museum. filter(lang(?englishabstract)='en')  optional{     ?museum dbpedia-owl:abstract ?russianabstract.     ?museum dbpedia-owl:museum. filter(lang(?russianabstract)='ru') }} group ?museum 

with query (that works good), find every row (museum) bunch of abstract in 2 languages: english , russian. russian abstracts present if available because use "optional". lot of empty attributes.

i replace blank attribute english abstract (always present).

reading w3c sparql page, found there particular testing value true when variable set: bound

i write this:

if bound (?russianabstract), "?russianabstract", "?englishabstract" 

--> if russianabstract present, hold it; else, put englishabstract instead of it.

does know how can make work?

one way use coalesce:

select  ?museum (coalesce(?russianabstract, ?englishabstract) ?abstract)