fix: related unit test

Author: maurei

src/JsonApiDotNetCore/Services/DefaultResourceService.cs

@@ -274,7 +274,10 @@ protected virtual IQueryable<TResource> ApplyInclude(IQueryable<TResource> entit
             {
                 foreach (var inclusionChain in chains)
                 {
-                    inclusionChain.InsertRange(0, chainPrefix);
+                    if (chainPrefix != null)
+                    {
+                        inclusionChain.InsertRange(0, chainPrefix);
+                    }
                     entities = _repository.Include(entities, inclusionChain.ToArray());
                 }
             }

test/UnitTests/Services/EntityResourceService_Tests.cs

@@ -87,7 +87,9 @@ public async Task GetRelationshipAsync_Returns_Relationship_Value()
 
         private DefaultResourceService<TodoItem> GetService()
         {
-            return new DefaultResourceService<TodoItem>(new List<IQueryParameterService>(), new JsonApiOptions(), _repositoryMock.Object, _resourceGraph);
+            var includeService = new Mock<IIncludeService>();
+            includeService.Setup(m => m.Get()).Returns(new List<List<RelationshipAttribute>>());
+            return new DefaultResourceService<TodoItem>(new List<IQueryParameterService>() { includeService.Object }, new JsonApiOptions(), _repositoryMock.Object, _resourceGraph);
         }
     }
 }