Mysterious nil values

[GrowthMindset]

How come print(item) from ModOnEquip outputs the item correctly upon item equip but print(item.prevslot) always outputs nil?

And why does print(item) from ModUnequip output nil when the item is right-clicked from the equip slot but outputs the item correctly when it is left-clicked instead?

local ENV = env
GLOBAL.setfenv(1, GLOBAL)

local function ModOnEquip(_, data)
    if type(data) == "table" and data.eslot and data.item then
        local item = data.item
        print(item)
        print(item.prevslot)
    end
end

local function ModOnUnequip(inst, data)
    if type(data) ~= "table" then return end
    local item = data.item
    print(item)
end

ENV.AddComponentPostInit("playercontroller", function(self)
    if self.inst ~= ThePlayer then return end
    self.inst:ListenForEvent("equip", ModOnEquip)
    self.inst:ListenForEvent("unequip", ModOnUnequip)

    local OnRemoveFromEntity = self.OnRemoveFromEntity
    self.OnRemoveFromEntity = function(self, ...)
        self.inst:RemoveEventCallback("equip", ModOnEquip)
        self.inst:RemoveEventCallback("unequip", ModOnUnequip)
        return OnRemoveFromEntity(self, ...)
    end
end)

I'm fairly new to modding (have made only one server mod so far, so I'm still analyzing stuff when it comes to client side mods). Can anyone please enlighten me about the above or give me related beginner-friendly guides?

Edited July 16, 2022 by GrowthMindset
some corrections