color2 is null loading outdoor-v2

[SilvioDallAcqua]

loading the outdoor-v2 map from maptiler:

		let group = new LayerGroup();
		apply(group, 'https://api.maptiler.com/maps/outdoor-v2/style.json?key=xxxxxxxxxxxxxxxx');
		map.getLayers().push(group);

leads to an error:

Other maps from maptiler do not show this error.
As a consequence, when zooming in, text-labels are shown for a very short time (0.1s) and disapears afterwards. For the rest the map is displayed correctly.

[ahocevar]

Thanks for reporting this, see #1094 for the fix.