How to prevent "Unable to cast double to Content"?

This script bellow is made to preload any assets within a model, and it works when there is just one of each item, but if there is more than on of an item (hat, decal ect.) it gets stuck and just says "ContentProvider:Preload() failed for " "Unable to cast double to Content" How can I prevent this?

local function WaitForAssetsToLoad()
    while (ContentProvider.RequestQueueSize > 0) do
        wait(0.1)
    end
end

local function LoadAssets(AssetList)
    for _, Asset in pairs(AssetList) do
        if Asset.ClassName == "StringValue" then
        ContentProvider:Preload(Asset.Value)
        elseif Asset.ClassName == "Sound" then
        ContentProvider:Preload(Asset.SoundId)
        elseif Asset.ClassName == "Decal" or Asset.ClassName == "Texture" then
        ContentProvider:Preload(Asset.Texture)
        elseif Asset.ClassName == "Animation" then
        ContentProvider:Preload(Asset.AnimationId)
        elseif Asset.ClassName == "Shirt" then
        ContentProvider:Preload(Asset.ShirtTemplate)
        elseif Asset.ClassName == "Pants" then
        ContentProvider:Preload(Asset.PantsTemplate)
        elseif Asset.ClassName == "ShirtGraphic" then
        ContentProvider:Preload(Asset.Graphic)
        elseif Asset.ClassName == "CharacterMesh" or Asset.ClassName == "SpecialMesh" then
        ContentProvider:Preload(Asset.MeshId)
        ContentProvider:Preload(Asset.TextureId)
        elseif Asset.ClassName == "ImageLabel" or Asset.ClassName == "ImageButton" then
        ContentProvider:Preload(Asset.Image)
        else        
        LoadAssets(Asset:GetChildren())
        end
    end 
    WaitForAssetsToLoad()
end