if (!(node.edges[0].contents instanceof SIRJoiner)) {
if (node.edges[0] == null || !(node.edges[0].contents instanceof SIRJoiner)) {
    public void visitNode(FlatNode node)     {	if (node.contents instanceof SIRFilter &&	    !(node.contents instanceof SIRFileReader)) {	    	    assigned.add(node);	    return;	}	if (node.contents instanceof SIRJoiner) {	    if (!(node.edges[0].contents instanceof SIRJoiner)) {		joiners.add(node);		assigned.add(node);		return;	    }	}    }