Error starting a workflow

[hackdna]

TypeError exception is sometimes raised when trying to run a workflow from Available Samples page.

Steps to reproduce:

1. Import an ISA-Tab file.
2. Proceed to the Available Samples page.
3. Select a workflow and its inputs, and click Run Workflow.

Analysis Results page loads but progress bars are not displayed. Data is not imported in Galaxy. No errors appear in Django server console but the following output appears in Celery console:

[2012-07-13 17:52:40,053: WARNING/PoolWorker-1] analysis_manager.chord_postprocessing called
[2012-07-13 17:52:40,065: WARNING/PoolWorker-1] analysis_manger.download_history_files called
[2012-07-13 17:52:40,122: ERROR/MainProcess] Task analysis_manager.tasks.chord_postprocessing[d5c88166-9d1d-47ac-bacc-375b950cd927] raised exception: TypeError("cannot concatenate 'str' and 'NoneType' objects",)
Traceback (most recent call last):
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/execute/trace.py", line 47, in trace
    return cls(states.SUCCESS, retval=fun(*args, **kwargs))
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/app/task/__init__.py", line 247, in __call__
    return self.run(*args, **kwargs)
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/app/__init__.py", line 175, in run
    return fun(*args, **kwargs)
  File "/Users/isytchev/workspace/Refinery/refinery/analysis_manager/tasks.py", line 74, in chord_postprocessing
    postprocessing_taskset = download_history_files(analysis)
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/app/task/__init__.py", line 247, in __call__
    return self.run(*args, **kwargs)
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/app/__init__.py", line 175, in run
    return fun(*args, **kwargs)
  File "/Users/isytchev/workspace/Refinery/refinery/analysis_manager/tasks.py", line 399, in download_history_files
    download_list = connection.get_history_file_list(analysis.history_id)
  File "/Users/isytchev/workspace/Refinery/refinery/galaxy_connector/connection.py", line 124, in get_history_file_list
    print self.get_history_contents( history_id )
  File "/Users/isytchev/workspace/Refinery/refinery/galaxy_connector/connection.py", line 98, in get_history_contents
    return self.get( "histories" + "/" + history_id + "/" + "contents" )
TypeError: cannot concatenate 'str' and 'NoneType' objects

Traceback (most recent call last):
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/execute/trace.py", line 47, in trace
    return cls(states.SUCCESS, retval=fun(*args, **kwargs))
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/app/task/__init__.py", line 247, in __call__
    return self.run(*args, **kwargs)
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/app/__init__.py", line 175, in run
    return fun(*args, **kwargs)
  File "/Users/isytchev/workspace/Refinery/refinery/analysis_manager/tasks.py", line 74, in chord_postprocessing
    postprocessing_taskset = download_history_files(analysis)
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/app/task/__init__.py", line 247, in __call__
    return self.run(*args, **kwargs)
  File "/Users/isytchev/environments/refinery/lib/python2.7/site-packages/celery/app/__init__.py", line 175, in run
    return fun(*args, **kwargs)
  File "/Users/isytchev/workspace/Refinery/refinery/analysis_manager/tasks.py", line 399, in download_history_files
    download_list = connection.get_history_file_list(analysis.history_id)
  File "/Users/isytchev/workspace/Refinery/refinery/galaxy_connector/connection.py", line 124, in get_history_file_list
    print self.get_history_contents( history_id )
  File "/Users/isytchev/workspace/Refinery/refinery/galaxy_connector/connection.py", line 98, in get_history_contents
    return self.get( "histories" + "/" + history_id + "/" + "contents" )
TypeError: cannot concatenate 'str' and 'NoneType' objects