fix tables unable to sort on nil dates

lib/cannery/comparable_date.ex

@@ -0,0 +1,12 @@
+defmodule Cannery.ComparableDate do
+  @moduledoc """
+  A custom `Date` module that provides a `compare/2` function that is comparable
+  with nil values
+  """
+
+  @spec compare(Date.t() | any(), Date.t() | any()) :: :lt | :gt | :eq
+  def compare(%Date{} = date_1, %Date{} = date_2), do: Date.compare(date_1, date_2)
+  def compare(%Date{}, _date_2), do: :lt
+  def compare(_date_1, %Date{}), do: :gt
+  def compare(_date_1, _date_2), do: :eq
+end