[10.x] Fix whereHasMorph() with nullable morphs (#48903)

* Support nullable morphs in whereHasMorph()

* Expand the whereHasMorph with nullable morph by using a sub condition

* Support nullable morphs in whereDoesntHaveMorph and orWhereHasMorph

* Fix testOrWhereHasMorphWithWildcardAndOnlyNullMorphTypes so there are no morph types in the database

Author: MarkKremer

src/Illuminate/Database/Eloquent/Concerns/QueriesRelationships.php

@@ -230,6 +230,10 @@ public function hasMorph($relation, $types, $operator = '>=', $count = 1, $boole
             $types = $this->model->newModelQuery()->distinct()->pluck($relation->getMorphType())->filter()->all();
         }
 
+        if (empty($types)) {
+            return $this->where(new Expression('0'), $operator, $count, $boolean);
+        }
+
         foreach ($types as &$type) {
             $type = Relation::getMorphedModel($type) ?? $type;
         }

tests/Integration/Database/EloquentWhereHasMorphTest.php

@@ -27,7 +27,7 @@ protected function defineDatabaseMigrationsAfterDatabaseRefreshed()
 
         Schema::create('comments', function (Blueprint $table) {
             $table->increments('id');
-            $table->morphs('commentable');
+            $table->nullableMorphs('commentable');
             $table->softDeletes();
         });
 
@@ -41,6 +41,8 @@ protected function defineDatabaseMigrationsAfterDatabaseRefreshed()
         $models[] = Video::create(['title' => 'foo']);
         $models[] = Video::create(['title' => 'bar']);
         $models[] = Video::create(['title' => 'baz']);
+        $models[] = null; // deleted
+        $models[] = null; // deleted
 
         foreach ($models as $model) {
             (new Comment)->commentable()->associate($model)->save();
@@ -103,6 +105,19 @@ public function testWhereHasMorphWithWildcardAndMorphMap()
         }
     }
 
+    public function testWhereHasMorphWithWildcardAndOnlyNullMorphTypes()
+    {
+        Comment::whereNotNull('commentable_type')->forceDelete();
+
+        $comments = Comment::query()
+            ->whereHasMorph('commentable', '*', function (Builder $query) {
+                $query->where('title', 'foo');
+            })
+            ->orderBy('id')->get();
+
+        $this->assertEmpty($comments->pluck('id')->all());
+    }
+
     public function testWhereHasMorphWithRelationConstraint()
     {
         $comments = Comment::whereHasMorph('commentableWithConstraint', Video::class, function (Builder $query) {
@@ -190,6 +205,18 @@ public function testOrWhereHasMorph()
         $this->assertEquals([1, 4], $comments->pluck('id')->all());
     }
 
+    public function testOrWhereHasMorphWithWildcardAndOnlyNullMorphTypes()
+    {
+        Comment::whereNotNull('commentable_type')->forceDelete();
+
+        $comments = Comment::where('id', 7)
+            ->orWhereHasMorph('commentable', '*', function (Builder $query) {
+                $query->where('title', 'foo');
+            })->orderBy('id')->get();
+
+        $this->assertEquals([7], $comments->pluck('id')->all());
+    }
+
     public function testWhereDoesntHaveMorph()
     {
         $comments = Comment::whereDoesntHaveMorph('commentable', Post::class, function (Builder $query) {
@@ -199,6 +226,17 @@ public function testWhereDoesntHaveMorph()
         $this->assertEquals([2, 3], $comments->pluck('id')->all());
     }
 
+    public function testWhereDoesntHaveMorphWithWildcardAndOnlyNullMorphTypes()
+    {
+        Comment::whereNotNull('commentable_type')->forceDelete();
+
+        $comments = Comment::whereDoesntHaveMorph('commentable', [], function (Builder $query) {
+            $query->where('title', 'foo');
+        })->orderBy('id')->get();
+
+        $this->assertEquals([7, 8], $comments->pluck('id')->all());
+    }
+
     public function testOrWhereDoesntHaveMorph()
     {
         $comments = Comment::where('id', 1)