[6.x] Skip empty-list lookups in the Entries fieldtype and Stache whereIn"

src/Fieldtypes/Entries.php

@@ -519,6 +519,11 @@ public function getColumns()
 
     protected function getItemsForPreProcessIndex($values): SupportCollection
     {
+        // Nothing selected, so there's nothing to go looking for.
+        if (empty(Arr::wrap($values))) {
+            return $this->collect([]);
+        }
+
         // These are the entries a query for them in any status would find, so they aren't looked for a second time.
         return Entry::applySubstitutions($this->entriesInTheirSite($values)->unique->id()->values());
     }

src/Stache/Query/Builder.php

@@ -191,6 +191,11 @@ private function comparesEqualityAsStrings($where)
 
     protected function filterWhereIn($values, $where)
     {
+        // Nothing can be in an empty list.
+        if (empty($where['values'])) {
+            return $values->take(0);
+        }
+
         $lookup = array_flip(array_map($this->normalizeLookupValue(...), $where['values']));
 
         return $values->filter(

tests/Data/Entries/EntryQueryBuilderTest.php

@@ -77,6 +77,17 @@ public function entries_are_found_using_or_where_in()
         $this->assertEquals(['Post 1', 'Post 2', 'Post 4', 'Post 5'], $entries->map->title->all());
     }
 
+    #[Test]
+    public function nothing_is_found_in_an_empty_list()
+    {
+        $this->createDummyCollectionAndEntries();
+
+        $this->assertSame([], Entry::query()->whereIn('id', [])->get()->map->id()->all());
+        $this->assertSame([], Entry::query()->whereIn('title', [])->get()->map->id()->all());
+        $this->assertSame(['id-1'], Entry::query()->where('title', 'Post 1')->orWhereIn('id', [])->get()->map->id()->all());
+        $this->assertSame(['id-1', 'id-2', 'id-3'], Entry::query()->whereNotIn('id', [])->get()->map->id()->all());
+    }
+
     #[Test]
     public function entries_are_ordered_the_way_a_data_collection_sorts_their_values()
     {

tests/Fieldtypes/EntriesTest.php

@@ -134,6 +134,17 @@ public function it_returns_empty_collection_when_preprocessing_index_and_max_ite
         $this->assertEquals([], $preProcessed->all());
     }
 
+    #[Test]
+    public function it_returns_an_empty_collection_when_preprocessing_index_and_nothing_is_selected()
+    {
+        foreach ([null, []] as $value) {
+            $preProcessed = $this->fieldtype()->preProcessIndex($value);
+
+            $this->assertInstanceOf(Collection::class, $preProcessed);
+            $this->assertCount(0, $preProcessed);
+        }
+    }
+
     #[Test]
     public function it_includes_drafts_when_pre_processing_for_index()
     {