using IF statement to check if, dataStream has some values in Apache Flink -

i generating warnings in cep follows

  // generating warnings    datastream<joinedstreamevent> warning = patternstream.select(           (map<string, joinedstreamevent> value) ->                     {        joinedstreamevent joinedstreamevent = (joinedstreamevent) value.get("start");        return  new joinedstreamevent(joinedstreamevent.getpatient_id(), joinedstreamevent.getheartrate(),joinedstreamevent.getrespirationrate());                      }// map             ); 

then printing warnings later console, however, want add if statement check, if complex event has been detected or not , perform tasks in if statement

for instance, want print complex events detected follows , show complex events detected following code

if( warning.tostring() != null){    system.out.println("complex events detected follows : -");   warning.print();      } 

here complex event 10,71,71 , output shown follows

i assume logic check if data stream has value in if statement wrong.that reason line "complex events detected follows: -" getting printed first

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is there way that, can check whether datastream has values using if statement , print vlaues. in case, output

complex events detected follows : -  10,71,71 

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