Empty value in a set

Hello,

I have the following code and I would like to be able to evaluate a “null or empty” value in a position. I’ve been trying with the null function.

{int} conjuPred [h in 1..2, i in 1..5] = [  [ {} {1} {2} {2} {4} ]                                                             [ {} {1} {} {} {} ]  ] ;

string phi = “Bad”;
execute{
     if (conjunPred[1][1] == null){
              phi = “Good”;
     }  
}
execute{
    writeln(“Result: “+phi)
}

 ¿ What would be the correct function to be able to enter to the “if” conditional ?

Many thanks in advance.

Best Regards.