PSE Isocline does not start when Group of TS is left alone

To reproduce:

• create a 2D PSE group of TVB results
• remove GroupofMeasures
• try to launch PSE Isocline on the remaining GroupOfTS
• the following error will be thrown:

  2017-12-22 09:00:17,679 - ERROR - tvb.core.services.operation_service - No datatypes were generated due to simulation errors. Nothing to display.
  Traceback (most recent call last):
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/core/services/operation_service.py", line 333, in initiate_prelaunch
      result_msg, nr_datatypes = adapter_instance._prelaunch(operation, unique_id, available_space, **params)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/core/adapters/abcdisplayer.py", line 77, in _prelaunch
      return self.launch(**kwargs), 0
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/adapters/visualizers/pse_isocline.py", line 242, in launch
      params = self.get_metric_matrix(datatype_group)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/adapters/visualizers/pse_isocline.py", line 191, in get_metric_matrix
      self.model = PseIsoModel.from_db(datatype_group.fk_operation_group)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/adapters/visualizers/pse_isocline.py", line 70, in from_db
      PseIsoModel._find_metrics(operations), None)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/adapters/visualizers/pse_isocline.py", line 100, in _find_metrics
      raise LaunchException("No datatypes were generated due to simulation errors. Nothing to display.")
  LaunchException: No datatypes were generated due to simulation errors. Nothing to display.
  2017-12-22 09:00:17,709 - ERROR - tvb.core.services.flow_service - Could not launch operation IsoclinePSEAdapter with the given set of input data, because: No datatypes were generated due to simulation errors. Nothing to display.
  Traceback (most recent call last):
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/core/services/flow_service.py", line 175, in fire_operation
      tmp_folder, visible, **data)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/core/services/operation_service.py", line 152, in initiate_operation
      return self.initiate_prelaunch(operations[0], adapter_instance, temp_files, **kwargs)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/core/services/operation_service.py", line 348, in initiate_prelaunch
      self._handle_exception(excep, temp_files, excep.message, operation)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/core/services/operation_service.py", line 333, in initiate_prelaunch
      result_msg, nr_datatypes = adapter_instance._prelaunch(operation, unique_id, available_space, **params)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/core/adapters/abcdisplayer.py", line 77, in _prelaunch
      return self.launch(**kwargs), 0
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/adapters/visualizers/pse_isocline.py", line 242, in launch
      params = self.get_metric_matrix(datatype_group)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/adapters/visualizers/pse_isocline.py", line 191, in get_metric_matrix
      self.model = PseIsoModel.from_db(datatype_group.fk_operation_group)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/adapters/visualizers/pse_isocline.py", line 70, in from_db
      PseIsoModel._find_metrics(operations), None)
    File "/WORK/TVB/tvb-root/framework_tvb/tvb/adapters/visualizers/pse_isocline.py", line 100, in _find_metrics
      raise LaunchException("No datatypes were generated due to simulation errors. Nothing to display.")
  LaunchException: No datatypes were generated due to simulation errors. Nothing to display.