fix BelongsTo returns integer causing SQL to fail

Author: michaellee8-iclass

src/Illuminate/Database/Eloquent/Relations/BelongsTo.php

@@ -127,11 +127,10 @@ protected function getEagerModelKeys(array $models)
             }
         }
 
-        // If there are no keys that were not null we will just return an array with either
-        // null or 0 in (depending on if incrementing keys are in use) so the query wont
-        // fail plus returns zero results, which should be what the developer expects.
+        // If there are no keys that were not null we will just return an array with null
+        // so the query wont fail plus returns zero results, which should be what the developer expects.
         if (count($keys) === 0) {
-            return [$this->relationHasIncrementingId() ? 0 : null];
+            return [null];
         }
 
         sort($keys);

tests/Database/DatabaseEloquentBelongsToTest.php

@@ -103,7 +103,7 @@ public function testAssociateMethodSetsForeignKeyOnModelById()
     public function testDefaultEagerConstraintsWhenIncrementing()
     {
         $relation = $this->getRelation();
-        $relation->getQuery()->shouldReceive('whereIn')->once()->with('relation.id', m::mustBe([0]));
+        $relation->getQuery()->shouldReceive('whereIn')->once()->with('relation.id', m::mustBe([null]));
         $models = [new MissingEloquentBelongsToModelStub, new MissingEloquentBelongsToModelStub];
         $relation->addEagerConstraints($models);
     }