Nil error when trying to call a function in Lua

Nil error when trying to call a function in Lua

References

Reference NO 1

http://stackoverflow.com/questions/15192028/nil-error-when-trying-to-call-a-function-in-lua

Reference NO 2

http://stackoverflow.com/questions/10919626/lua-attempt-to-call-method-print-a-nil-value

Reference NO 3

http://www.lua.org/pil/8.3.html

Reference NO 4

http://www.computercraft.info/forums2/index.php?/topic/12471-luaerror-attempt-to-call-nil/

Reference NO 5

http://lua-users.org/wiki/FunctionsTutorial

Reference NO 6

http://maurits.tv/data/garrysmod/wiki/wiki.garrysmod.com/index5e8e.html

Reference NO 7

http://wiki.roblox.com/index.php/Lua_errors

Reference NO 8

https://github.com/FPtje/DarkRP/issues/122