Musescore crashed when call cursor.measure(); --- A MuseScore Bug?

I'm creating a plugin for MuseScore, And here is the code and the error I get.

function run() {
var cursor = new Cursor(curScore, true);
cursor.rewind();
while (!cursor.eos()) {

var height = 0;

try {
tick = cursor.tick();
var pos = cursor.pos();
var x = pos.x();
var y = pos.y();
print("tick="+tick);
if(cursor.isChord() || cursor.isRest()){
var measureType = typeof cursor.measure;
var measure = cursor.measure();
height = measure.boundingRect().height();
}
var s = "tick:" + tick + " point[" + x + "," + y + "] height=" + height;
print(s);
} catch (e) {
print(e);
}

cursor.next();
}
}

I have to check what cursor points to. otherwise, the plugin will corrupt MuseScore. I believe this should be caused by this piece of code in sccurosr.cpp.
case 4: // "measure",
if (context->argumentCount() == 0)
return qScriptValueFromValue(context->engine(), cursor->cr()->measure());
break;

since cursor call cursor->cr()->measure() directly, while cursor->cr() sometimes return null.

Also, It will be great if MuseScore can return a cursor if I provide a tick as parameter. And also, I believe, it's useful that a cursor always return a valid measure if the cursor really points to anything inside a measure.