why does my script get the error of Can't Parse JSON when using the HTTP service?

local HTTP = {}
HTTP.URL = "https://raw.githubusercontent.com/PixelLiten/Nethereal/master/0.0.1/files.json"
local http = game:GetService("HttpService")
function HTTP:HTTPGET(url)
	local success, res = pcall(http.RequestAsync, http, {
		Url = url;
		Method = "GET";
	})
	if (not success) then
		res = {
			Success = false;
			StatusCode = -1;
			StatusMessage = res;
			Headers = nil;
			Body = nil;
		}
	end
	if (not res.Success) then
		warn(url .. " >> " .. res.StatusMessage)
	end
	return res, res.Body
end
function HTTP:HTTPGETJSON(url)
	local success, res = pcall(http.RequestAsync, http, {
		Url = url;
		Method = "GET";
	})
	if (success) then
		local json
		success, json = pcall(http.JSONDecode, http, res.Body)
		if (success) then
			res.Body = json
		else
			res = json
		end
	end
	if (not success) then
		res = {
			Success = false;
			StatusCode = -1;
			StatusMessage = res;
			Headers = nil;
			Body = nil;
		}
	end
	if (not res.Success) then
		warn(url .. " >> " .. res.StatusMessage)
	end
	return res, res.Body
end
function HTTP:Install()
    warn "Fetching file list..."
	local filelistRes, filelist = self:HTTPGETJSON(self.URL)
	if (not filelistRes.Success) then
		warn(filelistRes.StatusMessage)
		return
	end
end
return HTTP