Roblox - error (New script) How do i fix it so that when you touch the person they give u the quest?

I'm making a quest system and I cannot seem to find what I did wrong

Here is the script:

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local QuestLibraries     = ReplicatedStorage:FindFirstChild("QuestLibraries")

     ----Libararies----
     local Dialogs = require(QuestLibraries:FindFirstChild("Dialogs"))
     local Quests  = require(QuestLibraries:FindFirstChild("Quests"))

     ----Varibles---
     local QuestGUI  = ReplicatedStorage:FindFirstChild("QuestDialog", true)
     local Quest        = script.configurations.Quest.Value
     local Enabled    = script.configurations.QuestEnabled.Value



    script.Parent.HumanoidRootPart.Touched:connect(function(hit)

if hit.Parent:FindFirstChild("Humanoid") ~= nil then

    local player    = game.Players:FindFirstChild(hit.Parent.Name)
    local playerGui = player:FindFirstChild("PlayerGui")

    if playerGui:FindFirstChild("QuestDialog") == nil then

        -----GUI parts-----         
        local GUI         = QuestGUI:Clone()
        local Main        = GUI.Hold.Hold.Frame
        local GUI_Name    = Main:FindFirstChild("TITLE", true)      
        local Decline_Btn = Main:FindFirstChild("Decline", true)
        local Accept_Btn  = Main:FindFirstChild("Accept", true)
        local NPC_Dialog  = Main:FindFirstChild("NPCDialog", true)

        ------Data Tables---
        local Dialog_Data = Dialogs.dialog[Quest]

        ------set defaluts--         
        GUI_Name.Text = " ".. script.Parent.Name

        GUI.Parent       = playerGui            
        Decline_Btn.Text = Dialog_Data["EXIT"]



        GUI.Parent = playerGui ------ puts gui into player gui
        --------- Get number of dialogs------

        local num_of_dialogs = 0

        for key, value in pairs(Dialog_Data) do
            if key ~= "EXIT" then
                num_of_dialogs = num_of_dialogs + 0.5

            end
        end
    end
    ----- Go Through Dialog-----
    local dialog_num = 1


    NPC_Dialog.Text = Dialog_Data["NPC" .. dialog_num]
    Accept_Btn.Text = Dialog_Data["RES" .. dialog_num]

    Accept_Btn.MouseButton1Click:connect(function()
            if dialog_num ~= num_of_dialogs then
                dialog_num = dialog_num + 1

                 NPC_Dialog.Text = Dialog_Data["NPC" .. dialog_num]
                 Accept_Btn.Text = Dialog_Data["RES" .. dialog_num]
            else
                GUI:Destroy()
            end
        end)

    end     

end)

Here is the error: Workspace.Lyden.QuestNPC:59: attempt to index global 'Dialog_Data' (a nil value)

Need Help Thank You!