It does not seem possible to execute an orchestrator workflow that requires no user input. (Example = all orchestrator workflow inputs are set as attributes). When the plugin has nothing to pass, the jenkins console reports there has been a "HTTP/1.1 400 Bad Request"

Jenkins Console Output:
07:35:15 Started by user anonymous
07:35:15 [EnvInject] - Loading node environment variables.
07:35:15 Building remotely on anonymous in workspace F:\jenkins\workspace\anonymous_orchestrator_jenkins_send_notification_null
07:35:16 Starting Orchestrator workflow execution : a18ceeea-e29e-4d04-8f73-4733e63f76d4
07:35:19 FATAL: Server responded with status code HTTP/1.1 400 Bad Request
07:35:19 java.io.IOException: Server responded with status code HTTP/1.1 400 Bad Request
07:35:19 at com.vmware.vro.jenkins.plugin.OrchestratorCallable.call(OrchestratorCallable.java:66)
07:35:19 at com.vmware.vro.jenkins.plugin.OrchestratorCallable.call(OrchestratorCallable.java:17)
07:35:19 at hudson.remoting.UserRequest.perform(UserRequest.java:121)
07:35:19 at hudson.remoting.UserRequest.perform(UserRequest.java:49)
07:35:19 at hudson.remoting.Request$2.run(Request.java:325)
07:35:19 at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:68)
07:35:19 at java.util.concurrent.FutureTask.run(Unknown Source)
07:35:19 at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
07:35:19 at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
07:35:19 at hudson.remoting.Engine$1$1.run(Engine.java:69)
07:35:19 at java.lang.Thread.run(Unknown Source)
07:35:19 at ......remote call to anonymous(Native Method)
07:35:19 at hudson.remoting.Channel.attachCallSiteStackTrace(Channel.java:1360)
07:35:19 at hudson.remoting.UserResponse.retrieve(UserRequest.java:221)
07:35:19 at hudson.remoting.Channel.call(Channel.java:753)
07:35:19 at com.vmware.vro.jenkins.plugin.OrchestratorBuilder.perform(OrchestratorBuilder.java:113)
07:35:19 at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
07:35:19 at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:761)
07:35:19 at hudson.model.Build$BuildExecution.build(Build.java:203)
07:35:19 at hudson.model.Build$BuildExecution.doRun(Build.java:160)
07:35:19 at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:536)
07:35:19 at hudson.model.Run.execute(Run.java:1741)
07:35:19 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
07:35:19 at hudson.model.ResourceController.execute(ResourceController.java:98)
07:35:19 at hudson.model.Executor.run(Executor.java:374)
07:35:19 Caused by: java.io.IOException: Server responded with status code HTTP/1.1 400 Bad Request
07:35:19 at com.vmware.vro.jenkins.plugin.util.RestClient.httpPostForLocationHeader(RestClient.java:105)
07:35:19 at com.vmware.vro.jenkins.plugin.OrchestratorClient.executeWorkflow(OrchestratorClient.java:135)
07:35:19 at com.vmware.vro.jenkins.plugin.OrchestratorCallable.call(OrchestratorCallable.java:31)
07:35:19 at com.vmware.vro.jenkins.plugin.OrchestratorCallable.call(OrchestratorCallable.java:17)
07:35:19 at hudson.remoting.UserRequest.perform(UserRequest.java:121)
07:35:19 at hudson.remoting.UserRequest.perform(UserRequest.java:49)
07:35:19 at hudson.remoting.Request$2.run(Request.java:325)
07:35:19 at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:68)
07:35:19 at java.util.concurrent.FutureTask.run(Unknown Source)
07:35:19 at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
07:35:19 at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
07:35:19 at hudson.remoting.Engine$1$1.run(Engine.java:69)
07:35:19 at java.lang.Thread.run(Unknown Source)
07:35:19 [BFA] Scanning build for known causes...
07:35:19 [BFA] No failure causes found
07:35:19 [BFA] Done. 0s
07:35:19 Started calculate disk usage of build
07:35:19 Finished Calculation of disk usage of build in 0 seconds
07:35:19 Started calculate disk usage of workspace
07:35:19 Finished Calculation of disk usage of workspace in 0 seconds
07:35:19 Finished: FAILURE

If the orchestrator workflow is run manually in workflow designer, the workflow runs successfully.