fix deserializer tests

Author: jaredcnance

src/JsonApiDotNetCore/Serialization/JsonApiDeSerializer.cs

@@ -283,13 +283,8 @@ private object SetHasManyRelationship(object entity,
 
             if (relationships.TryGetValue(relationshipName, out RelationshipData relationshipData))
             {
-                if(relationshipData.IsHasMany == false) {
-                    throw new JsonApiException(400, $"Cannot set HasMany relationship '{attr.PublicRelationshipName}'. Value must be a JSON array of Resource Identifier Objects.");
-                }
-
-                var data = (List<ResourceIdentifierObject>)relationshipData.ExposedData;
-
-                if (data == null) return entity;
+                if(relationshipData.IsHasMany == false || relationshipData.ManyData == null)
+                    return entity;
 
                 var relatedResources = relationshipData.ManyData.Select(r =>
                 {

test/JsonApiDotNetCoreExampleTests/Acceptance/TodoItemsControllerTests.cs

@@ -301,10 +301,10 @@ public async Task Can_Get_TodoItem_WithOwner()
             // Act
             var response = await _fixture.Client.SendAsync(request);
             var body = await response.Content.ReadAsStringAsync();
-            var deserializedBody = (TodoItem)_fixture.GetService<IJsonApiDeSerializer>().Deserialize(body);
 
             // Assert
             Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            var deserializedBody = (TodoItem)_fixture.GetService<IJsonApiDeSerializer>().Deserialize(body);
             Assert.Equal(person.Id, deserializedBody.OwnerId);
             Assert.Equal(todoItem.Id, deserializedBody.Id);
             Assert.Equal(todoItem.Description, deserializedBody.Description);