cannot convert '{ }' into '{ a: number? }' bug

[jackdotink]

export type function tblpartial(tbl: type)
	assert(tbl:is("table"), "tblpartial can only be applied to tables")
	local new = types.newtable()

	for k, v in tbl:properties() do
		local read = assert(v.read, "properties cannot be write-only")
		new:setreadproperty(k, types.optional(read))
	end

	return new
end

local function tblmerge<T>(base: T, override: tblpartial<T>): T error("unimplemented") end
tblmerge({ a = 1 }, {}) -- Type '{  }' could not be converted into '{ read a: number? }'

This code causes the type error commented on the last line. Expected behavior would be that there are no type errors here.