0 is not recognized as valid LESS selector.

[seven-phases-max]

The following snippet:

0 {
    property: value;
}

produces empty CSS output (tested online, version: 1.5.1b2).
Expected result:

0 {
    property: value;
}

More advanced example that also fails:

0, 1, 2, 3, 4 {
    x-& {
        p: v;
    }
}

[oyejorge]

Thanks!