presto-main/src/main/java/io/prestosql/operator/window/NthValueFunction.java/NthValueFunction/NthValueFunction
class NthValueFunction:    public NthValueFunction(List<Integer> argumentChannels, boolean ignoreNulls)
    {
        this.valueChannel = argumentChannels.get(0);
        this.offsetChannel = argumentChannels.get(1);
        this.ignoreNulls = ignoreNulls;
    }