AnalyzerAdapter.execute() method doesn't process null array correctly for AALOAD instruction

AnalyzerAdapter (visitInsn(Opcodes.AALOAD)) fails on the following valid Java
construction with ClassCastException: 

    Object[] arr = null;
    try {
        Object obj = arr[0];
    } catch(NullPointerException e) {
        // ...
    }

The reason is that AnalyzerAdapter.execute() method consider second stack value
as String for AALOAD instruction:

            case Opcodes.AALOAD:
                pop(1);
                t1 = pop();
                pushDesc(((String) t1).substring(1));
                break;

However in this case the second value on the stack (array type) will be
Opcodes.NULL which causes ClassCastException.

I'd suggest the following fix for this issue:
            case Opcodes.AALOAD:
                pop(1);
                t1 = pop();
                if (t1 instanceof String) {
                    pushDesc(((String) t1).substring(1));
                } else {
                    push("java/lang/Object");
                }
                break;