Simple After Effects Script that moves the markers from an AV layer to a new null layer.

MoveMarkersToNull.jsx

app.beginUndoGroup("Move Markers to Null"); //begins the undo group 

//Variables
var curItem = app.project.activeItem; //creates a variable that holds the selected comp
var curLayer = curItem.selectedLayers[0]; //creates a variable that holds the selected layer
var oldMarkers = curLayer.property("Marker");

function main()
{
  var nullLayer = curItem.layers.addNull(curItem.duration); //create our null object

	for (i=1; i<=oldMarkers.numKeys; i++)
	{
		nullLayer.property("Marker").setValueAtTime(oldMarkers.keyTime(i), oldMarkers.keyValue(i));
	}
}

main(); //main function

app.endUndoGroup();