Intermittent Test Failure

[jaredcnance]

[xUnit.net 00:00:01.5243554]     UnitTests.DocumentBuilder_Tests.Build_Will_Use_Instance_Specific_Resource_If_Defined_For_Multiple_Documents [FAIL]
Failed   UnitTests.DocumentBuilder_Tests.Build_Will_Use_Instance_Specific_Resource_If_Defined_For_Multiple_Documents
Error Message:
 System.NullReferenceException : Object reference not set to an instance of an object.
Stack Trace:
   at JsonApiDotNetCore.Models.ResourceDefinition`1.Remove(Expression`1 filter, List`1 from) in /home/travis/build/json-api-dotnet/JsonApiDotNetCore/src/JsonApiDotNetCore/Models/ResourceDefinition.cs:line 53
   at UnitTests.DocumentBuilder_Tests.InstanceSpecificUserResource.OutputAttrs(User instance) in /home/travis/build/json-api-dotnet/JsonApiDotNetCore/test/UnitTests/Builders/DocumentBuilder_Tests.cs:line 366
   at JsonApiDotNetCore.Models.ResourceDefinition`1.GetOutputAttrs(Object instance) in /home/travis/build/json-api-dotnet/JsonApiDotNetCore/src/JsonApiDotNetCore/Models/ResourceDefinition.cs:line 89
   at JsonApiDotNetCore.Builders.DocumentBuilder.GetData(ContextEntity contextEntity, IIdentifiable entity, IResourceDefinition resourceDefinition) in /home/travis/build/json-api-dotnet/JsonApiDotNetCore/src/JsonApiDotNetCore/Builders/DocumentBuilder.cs:line 126
   at JsonApiDotNetCore.Builders.DocumentBuilder.Build(IEnumerable`1 entities) in /home/travis/build/json-api-dotnet/JsonApiDotNetCore/src/JsonApiDotNetCore/Builders/DocumentBuilder.cs:line 70
   at UnitTests.DocumentBuilder_Tests.Build_Will_Use_Instance_Specific_Resource_If_Defined_For_Multiple_Documents() in /home/travis/build/json-api-dotnet/JsonApiDotNetCore/test/UnitTests/Builders/DocumentBuilder_Tests.cs:line 328