Summary:
JavaScript interpreter crashes if Array#sort arguments are re-used as variables.
e.g.

arr.sort(function(a, b) {
    a = transform(a);
    b = transform(b);
    return a == b ? 0 : a > b ? 1 : -1;
});

Expected result:
Array is sorted successfully

Actual result:
Qt application crashes with SEGFAULT and message:
file:///.../main.qml:23: TypeError: Cannot read property 'val' of null

Full code to reproduce this bug attached as main.qml.