fix Model::tryLoad usages in Reference::ref

Author: mvorisek

src/Reference/ContainsOne.php

@@ -94,8 +94,13 @@ public function ref(Model $ourModel, array $defaults = []): Model
             });
         }
 
+        $theirModelOrig = $theirModel;
         $theirModel = $theirModel->tryLoadOne();
 
+        if ($theirModel === null) { // TODO or implement tryRef?
+            $theirModel = $theirModelOrig->createEntity();
+        }
+
         return $theirModel;
     }
 }

src/Reference/HasOne.php

@@ -91,11 +91,16 @@ public function ref(Model $ourModel, array $defaults = []): Model
             $ourValue = $this->getOurFieldValue($ourModel);
             $this->assertReferenceValueNotNull($ourValue);
 
+            $theirModelOrig = $theirModel;
             if ($this->their_field) {
                 $theirModel = $theirModel->tryLoadBy($this->their_field, $ourValue);
             } else {
                 $theirModel = $theirModel->tryLoad($ourValue);
             }
+
+            if ($theirModel === null) { // TODO or implement tryRef?
+                $theirModel = $theirModelOrig->createEntity();
+            }
         }
 
         // their model will be reloaded after saving our model to reflect changes in referenced fields