Sort nil dates last in both directions

advances #272

solr/conf/schema.xml

@@ -181,7 +181,7 @@
     <dynamicField name="*_txtm_tr" type="text_tr"  indexed="true"  stored="true" multiValued="true"/>
 
     <dynamicField name="*_i"  type="pint"    indexed="true"  stored="true"/>
-    <dynamicField name="*_is" type="pints"    indexed="true"  stored="true"/>
+    <dynamicField name="*_is" type="pints"    indexed="true"  stored="true" sortMissingLast="true" />
     <dynamicField name="*_s"  type="string"  indexed="true"  stored="true" />
     <dynamicField name="*_ss" type="strings"  indexed="true"  stored="true"/>
     <dynamicField name="*_l"  type="plong"   indexed="true"  stored="true"/>

test/dpul_collections_web/live/search_live_test.exs

@@ -114,6 +114,48 @@ defmodule DpulCollectionsWeb.SearchLiveTest do
            |> Enum.empty?()
   end
 
+  test "when sorting by date, a nil date always sorts last", %{conn: conn} do
+    # {"id": "nildate", "title_txtm": "Document Nil Date"},
+    # {"id": "emptydate", "title_txtm": "Document Empty Date", "years_is": []}
+    Solr.add(
+      [
+        %{
+          id: "nildate",
+          title_txtm: "Document-nildate"
+        },
+        %{
+          id: "emptydate",
+          title_txtm: "Document-emptydate",
+          years_is: []
+        }
+      ],
+      active_collection()
+    )
+
+    Solr.commit()
+
+    {:ok, view, html} = live(conn, "/search?sort_by=date_desc&page=11")
+    {:ok, document} = Floki.parse_document(html)
+
+    assert document
+           |> Floki.find(~s{a[href="/i/documentnildate/item/nildate"]})
+           |> Enum.any?()
+
+    assert document
+           |> Floki.find(~s{a[href="/i/documentemptydate/item/emptydate"]})
+           |> Enum.any?()
+
+    {:ok, view, document} = live(conn, "/search?sort_by=date_asc&page=11")
+
+    assert document
+           |> Floki.find(~s{a[href="/i/documentnildate/item/nildate"]})
+           |> Enum.any?()
+
+    assert document
+           |> Floki.find(~s{a[href="/i/documentemptydate/item/emptydate"]})
+           |> Enum.any?()
+  end
+
   test "items can be filtered by date range", %{conn: conn} do
     {:ok, view, _html} = live(conn, "/search")