Why doesn't my script get the object the mouse points to?

Hey. I wanna' do a Grapple Hook that activates when I press F and takes you to the object your mouse is on. I got the script working and all(like if I want to grapple to a specific part everything works) but when I try it with the mouse it says Workspace.bruceywayne.NEW:25: attempt to index field 'Target' (a nil value) and I don't know why. This is the script:

player = game.Players.LocalPlayer
mouse = player:GetMouse()
target = mouse.Target

activated = true

local character = game.Players.LocalPlayer.Character
Humanoid = character.Humanoid

local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/Asset?ID=01231272033"

local animation2 = Instance.new("Animation")
animation2.AnimationId = "http://www.roblox.com/Asset?ID=01231293787"

local animTrack = Humanoid:LoadAnimation(animation)
local animTrack2 = Humanoid:LoadAnimation(animation2)

local GrappleSound = Instance.new("Sound", workspace)
GrappleSound.SoundId = "http://www.roblox.com/Asset?ID=996815728"
GrappleSound.Volume = 1

mouse.KeyDown:Connect(function(key)
    for i, v in pairs(game.Players:GetChildren()) do
        if (v.Character.UpperTorso.Position - mouse.Target.Position).magnitude <= 100 then
            if string.lower(key) == 'f' and activated == true then
                local Grapple = game.Players.LocalPlayer.Character.rhand
                if character and character:findFirstChild("Humanoid") then
                    Grapple.Union.Transparency = 0
                    activated = false
                    animTrack:Play()
                    GrappleSound:Play()
                    local partA = Grapple.PartA
                    local attachmentA = Instance.new("Attachment", partA)
                    attachmentA.Position = Vector3.new(0, 0, -1)

                    local partB = target
                    local attachmentB = Instance.new("Attachment", partB)
                    attachmentB.Position = Vector3.new(0, .5, 0)

                    local Rope = Humanoid.Parent.rhand.Beam
                    Rope.Attachment0 = attachmentA
                    Rope.Attachment1 = attachmentB
                    Rope.Segments = 1
                    Rope.Width0 = 0.3
                    Rope.Width1 = 0.3

                    wait(1)

                    animTrack:Stop()
                    animTrack2:Play()

                    local b = Instance.new("BodyPosition")
                    b.position = mouse.Target.Position
                    b.maxForce = Vector3.new(500000000, 500000000, 500000000)
                    b.Parent = character.UpperTorso 

                    wait(1.5)

                    Rope.Attachment0 = nil
                    Rope.Attachment1 = nil
                    b.Parent = nil
                    activated = true
                    animTrack2:Stop()
                    Grapple.Union.Transparency = 1
                end
            end
        end
    end
end)