Getting findBestList

I am trying to get the best pic out of a list of pics. Using this page as reference :-
sikulix-2014.readthedocs.io/en/latest/region.html#Region.exists
But am getting:-
Runtime error: attempt to call global 'findBestList' (a nil value).
From what I understand is that, the code is unable to find - findBestList(<list>) method. Do I need to add any library from sikulix to make it work???

Here is the code
-- ========== Settings ================
Settings:setCompareDimension(true, 1065)
Settings:setScriptDimension(true, 1065)
Settings:set("MinSimilarity", 0.85)
-- ========== main program ===========
allLevels = {"EmptyPlot.png","ResLvl01.png","ResLvl02.png","ResLvl03.png","ResLvl04.png","ResLvl05.png","ResLvl06.png","ResLvl07.png","ResLvl08.png","ResLvl09.png"}

function findCurrentLevel()
indexFoundAt = 0
match = findBestList(allLevels)
if match then
print ("found img" .. match.getIndex())
indexFoundAt = match.getIndex()
end
return indexFoundAt
end

print("findCurrentLevel(10) = " .. findCurrentLevel(10))