IOException in ProcessBuilder.start method during compile

Process runProgram(List<String> args) {                  
    ProcessBuilder pb = new ProcessBuilder(args);        
    return pb.start();                                   

When I try to compile and run with processing-java.exe --sketch … --run I see error when loading my code. Mind you, no execution path gets to above code during loading. Yet I still get what seems like a runtime error:

foo.pde:745:0:745:0: Unhandled exception type IOException

If I comment out pb.start() call, it compiles and loads just fine. Same IOException when using Runtime.exec instead. How do I get a runtime IOException when compiling these statements?