Object reference not set to an instance of an object registering Custom Api

[twiga2013]

I am currently on using spkl 1.0.640 when I try to register a custom API with the following attribute I am getting the following error message

Here is the registration

[CrmPluginRegistration("Boza.DocumentStorageProviderPlugin")]
public class DocumentStorageProviderPlugin : PluginBase

The application terminated with an error.
Object reference not set to an instance of an object.
at SparkleXrm.Tasks.Reflection.<>c.b__4_2(CrmPluginRegistrationAttribute s)
at System.Linq.Lookup2.Create[TSource](IEnumerable1 source, Func2 keySelector, Func2 elementSelector, IEqualityComparer1 comparer) at System.Linq.GroupedEnumerable3.GetEnumerator()
at System.Linq.Enumerable.d__172.MoveNext() at System.Linq.Enumerable.Count[TSource](IEnumerable1 source)
at SparkleXrm.Tasks.Reflection.GetAttributes(IEnumerable1 types, String attributeName) at SparkleXrm.Tasks.PluginRegistraton.RegisterAssembly(FileInfo assemblyFilePath, Assembly assembly, IEnumerable1 pluginTypes, Boolean isWorkflowActivity)
at SparkleXrm.Tasks.PluginRegistraton.RegisterPlugin(String file, Boolean excludePluginSteps)
at SparkleXrm.Tasks.DeployPluginsTask.DeployPlugins(OrganizationServiceContext ctx, ConfigFile config)
at SparkleXrm.Tasks.DeployPluginsTask.ExecuteInternal(String folder, OrganizationServiceContext ctx)
at SparkleXrm.Tasks.BaseTask.Execute(String folder)
at SparkleXrmTask.Program.RunTask(CommandLineArgs arguments, IOrganizationService service, ITrace trace)
at SparkleXrmTask.Program.Run(CommandLineArgs arguments)
at SparkleXrmTask.Program.Main(String[] args)
Error Code=1