Object oriented programming, LUA help please!?

This script is in my module(s):

Person = {}
Person.__index = Person

Person.martialArts = {}

function Person.new(name, age, ethnicity)
	local newPerson = {}
	setmetatable(newPerson,Person)
	Person.Name = name
	Person.Age = age
	Person.Ethnicity = ethnicity
	return newPerson
end

-- This is the area that is of problem, concern:
function Person.martialArts.new(style)
	local newMartialArts = {}
	setmetatable(newMartialArts,Person.martialArts)
	style = {}
	table.insert(Person.martialArts,style)
	return newMartialArts
end
-- This area!

function Person:Swim()
	print(self.Name.. " is swimming!")
end

return Person

See where I commented? This is the local script where I'm using this script/code:

Person = require(game.ReplicatedStorage.OOP)
local John = Person.new("John", "Young", "Human")
John.martialArts.new("Karate")
print(John.martialArts.Karate)

I'm trying to have it create a table called "Karate" inside martialArts for this particular person. But it won't create it and when it goes to print, the print says "nil." I don't know what I'm doing wrong.

For instance if I do John.martialArts.new("Karate") it should create the table "Karate" inside martialArts for John.

However, when doing print(John.martialArts.Karate), I simply get nil (whereas I should get an empty table value). Help?