this.cfg = cfg;
this.visitor = new IsNullValueFrameModelingVisitor(methodGen.getConstantPool());
	public IsNullValueAnalysis(MethodGen methodGen, CFG cfg, ValueNumberDataflow vnaDataflow) {		this.methodGen = methodGen;		this.cfg = cfg;		this.vnaDataflow = vnaDataflow;		this.numNonExceptionSuccessorMap = new int[cfg.getNumBasicBlocks()];		// For each basic block, calculate the number of non-exception successors.		Iterator<Edge> i = cfg.edgeIterator();		while (i.hasNext()) {			Edge edge = i.next();			if (edge.isExceptionEdge())				continue;			int srcBlockId = edge.getSource().getId();			numNonExceptionSuccessorMap[srcBlockId]++;		}	}