Java, NullPointerException on a matrix of object : I know the answer may be stupid, but I can't find the solution.
I am tring to use a matrix of object like this

    //static declaration (class attribute)
    static Litteral [] [] explicitsPropagations;
    ...
    //initialisation (sat and csp are declared)
    explicitsPropagations = new Litteral[csp.nbVar()][sat.nbVar()*2];
    ...
    //affectation (NullPointerException), idClause, iEP, iX are correctly declared

    for (int i = 0 ; i < iX ; i++)
		explicitsPropagations[idClause][iEP[idClause]] = X[i];
			
Can someone see the problem ?
Thanks.