Gracefully handle missing tasks.

attract/tasks/routes.py

@@ -1,3 +1,4 @@
+import json
 import logging
 
 from flask import Blueprint, render_template, request, current_app
@@ -6,6 +7,7 @@ import flask_login
 import werkzeug.exceptions as wz_exceptions
 
 import pillarsdk
+import pillarsdk.exceptions as sdk_exceptions
 from pillar.web.system_util import pillar_api
 import pillar.api.utils
 import pillar.web.subquery
@@ -63,7 +65,22 @@ def view_task(project, attract_props, task_id):
         raise wz_exceptions.Forbidden()
 
     api = pillar_api()
+    try:
         task = pillarsdk.Node.find(task_id, api=api)
+    except sdk_exceptions.ResourceNotFound as ex:
+        content = getattr(ex, 'content', None)
+        if content:
+            deleted_task = json.loads(content)
+            if deleted_task and deleted_task.get('_deleted', False):
+                # This task used to exist, but doesn't any more. Let the user know.
+                task_name = deleted_task.get('name')
+                if task_name:
+                    description = u'Task "%s" was deleted.' % task_name
+                else:
+                    description = u'This task was deleted.'
+                return render_template('errors/404_embed.html', description=description), 404
+        raise
+
     node_type = project.get_node_type(node_type_task['name'])
 
     # Fetch project users so that we can assign them tasks