Why this OnServerEvent paramenters aren't exactly how in FireServer()?

Hello, devs!

Title might be hard to understand, but I'll try to make you understand my problem. So I was trying to animate First Person Shooter and made script that will fire server into RemoteEvent when left mouse button pressed and then script will collect it by OnServerEvent but parameters send by FireServer(parameters) aren't same as OnServerEvent(parameters). I used player before using my parameter. There is no errors on output. Thanks in advice.

CODE:

Local Script

local player = game.Players.LocalPlayer

local mouse = player:GetMouse()

mouse.Button1Down:Connect(function()
    game.ReplicatedStorage.Shot:FireServer(player, workspace.Camera)
end)

Script

local anim = script.ShotAnim

game.ReplicatedStorage.Shot.OnServerEvent:Connect(function(player, cam)
    print(cam.Name .." ".. player.Name)
    local human = cam:WaitForChild("Arms"):FindFirstChild("Humanoid")
    local shot = human:LoadAnimation(anim)
    shot:Play()
end)

OUTPUT:

No errors

MyUsername MyUsername

DETAILS

Local Script located in StarterCharacterScripts and sends signal, Script located in workspace and collects signal, but something is wrong with parameters.

EDIT:

I removed player in parameters of FireServer() but then it prints out:

Workspace.ShotEvent:4: attempt to index nil with 'Name'

EDIT2:

I edited script to:

local anim = script.ShotAnim

game.ReplicatedStorage.Shot.OnServerEvent:Connect(function(player, cam)
    if cam then
        local human = cam:WaitForChild("Arms"):FindFirstChild("Humanoid")
        local shot = human:LoadAnimation(anim)
        shot:Play()
    else
        print("Doesn't work.")
    end
end)

It prints out "Doesn't work." on output.

EDIT3:

I edited script to:

local anim = script.ShotAnim

game.ReplicatedStorage.Shot.OnServerEvent:Connect(function(player, cam)
    print(cam)
    local human = cam:WaitForChild("Arms"):FindFirstChild("Humanoid")
    local shot = human:LoadAnimation(anim)
    shot:Play()
    print("Doesn't work.")
end)

EDIT3 OUTPUT:

nil

Workspace.ShotEvent:5: attempt to index nil with 'WaitForChild'