Having problem with getPreference and setPreferences in corona - lua

Question

I have been following the tutorials on corona website and everything has been going well so far.
But in the tutorial "Displaying and saving score" i seem to have the following runtime error.
attempt to call field setPreferences' (a nil value)
This is the code of score.lua
local M = {}
M.score = 0
function M.init( options )
local customOptions = options or {} -- nice use of "or" operator
local opt = {}
opt.fontSize = customOptions.fontSize or 24
opt.font = customOptions.font or native.systemFont
opt.x = customOptions.x or display.contentCenterX
opt.y = customOptions.y or opt.fontSize*0.5 -- such that the score is positioned at the top, half of its font size.
opt.maxDigits = customOptions.maxDigits or 6
opt.leadingZeros = customOptions.leadingZeros or false
local prefix = ""
if ( opt.leadingZeros ) then
prefix = "0"
end
M.format = "%" .. prefix .. opt.maxDigits .. "d" -- so that its accesible in other modules.
-- Create the score display object
M.scoreText = display.newText( string.format( M.format, 0 ), opt.x, opt.y, opt.font, opt.fontSize ) -- string.format() works like printf and scanf statements
M.scoreText:setFillColor(1,0,0)
return M.scoreText
end
function M.set( value )
M.score = tonumber(value)
M.scoreText.text = string.format( M.format, M.score )
end
function M.get()
return M.score
end
function M.add( amount )
M.score = M.score + tonumber(amount)
M.scoreText.text = string.format( M.format, M.score )
end
function M.save()
print (" the score is " .. M.score)
local saved = system.setPreferences( "app", { currentScore=M.score } )
if ( saved == false) then
print ( "ERROR: could not save score" )
end
end
function M.load()
local score = system.getPreference( "app", "currentScore", "number" )
if ( score ) then
return tonumber(score)
else
print( "ERROR: could not load score (score may not exist in storage)" )
end
end
return M
This is the code of main.lua
local score = require( "score" )
local scoreText = score.init(
{
fontSize = 20,
font = "CoolCustomFont.ttf",
x = display.contentCenterX,
y = 30,
maxDigits = 7,
leadingZeros = true
})
local savedScore = score.load()
score.set( 1000 ) -- Sets the score to value
score.save()
I am aware there are other ways of keeping score, but I want to know what the problem is in my code. I googled everywhere but couldn't come up with any solution. Maybe I have made a mistake somewhere that I'm not able to identify.
Even tried a build on my smart phone, but ended up getting the same error.

Answer 1

From corona docs
Syntax
system.setPreferences( category, preferences )
category (required)
String. Indicates which set of preferences should be accessed on the system. Currently, only the "app" category is supported — this is the application's custom preferences defined by the Corona app developer.
preferences (required)
Table. Table of preferences to be written to storage. This table should contain key-value pairs where the key is the unique name of the preference and its value is either a boolean, number, or string.
if your M.score is nil then you might get an error
try this
local saved = system.setPreferences( "app", { currentScore=M.score or 0 } )