std.traits.CommonType does not correctly handle the situation of one single value (non-type) parameter, i.e. CommonType!3.
Solution here:

template CommonType(T...)
{
    static if (!T.length)
        alias void CommonType;
    else static if (T.length == 1)
	{
        static if (is(typeof(T[0])))
            alias typeof( T[0] ) commonOrSingleType;
        else
            alias T[0] commonOrSingleType;
    }
    else static if (is(typeof(true ? T[0].init : T[1].init) U))
        alias CommonType!(U, T[2 .. $]) CommonType;
    else
        alias void CommonType;
}