check for deleted project

pycs/util/PipelineCache.py

@@ -116,6 +116,10 @@ class PipelineCache(GreenWorker):
                 continue
 
             project = Project.query.get(project_id)
+            if project is None:
+                # project does not exist anymore
+                continue
+
             # create job to close pipeline
             self.__jobs.run(project,
                             'Model Interaction',