crash when a property like material or position is null

[macrozone]

if you set material to null, app crashes with:

Exception '-[NSNull objectForKeyedSubscript:]: unrecognized selector sent to instance 0x1b4b31650' was thrown while invoking addPlane on target ARGeosManager with params (
        {
        material = "<null>";
        shape =         {
            height = "2.7";
            width = 0;
        };
    },
        {
        eulerAngles =         {
            x = 0;
            y = "1.570796326794897";
            z = 0;
        };
        id = "wall_0";
        position =         {
            x = 0;
            y = "1.35";
            z = 0;
        };
    },
    "<null>"
)