Network interdiction problems are broken

[stigrs]

I get the following error when I try to run, e.g., the min_cost_flow_interdict example:

`MultiIndex([( 'B', 'End'),
( 'C', 'B'),
( 'C', 'D'),
( 'D', 'End'),
('Start', 'B'),
('Start', 'C')],
names=['StartNode', 'EndNode'])
ERROR: Constructing component 'edge_set' from data=None failed: ValueError:
The truth value of a MultiIndex is ambiguous. Use a.empty, a.bool(),
a.item(), a.any() or a.all().

ValueError Traceback (most recent call last)
in
227
228 if name == 'main':
--> 229 m = MinCostFlowInterdiction('sample_nodes_data.csv', 'sample_arcs_data.csv')
230 m.solve()
231 m.printSolution()

in init(self, nodefile, arcfile, attacks)
44 self.nCmax = len(self.node_set) * self.arc_data['Cost'].max()
45
---> 46 self.createPrimal()
47 self.createInterdictionDual()
48

in createPrimal(self)
59 # Add the sets
60 model.node_set = pe.Set( initialize=self.node_set )
---> 61 model.edge_set = pe.Set( initialize=self.arc_set, dimen=2)
62
63 # Create the variables

C:\Program Files (x86)\Microsoft Visual Studio\Shared\Anaconda3_64\lib\site-packages\pyomo\core\base\block.py in setattr(self, name, val)
541 # Pyomo components are added with the add_component method.
542 #
--> 543 self.add_component(name, val)
544 else:
545 #

C:\Program Files (x86)\Microsoft Visual Studio\Shared\Anaconda3_64\lib\site-packages\pyomo\core\base\block.py in add_component(self, name, val)
1079 _blockName, str(data))
1080 try:
-> 1081 val.construct(data)
1082 except:
1083 err = sys.exc_info()[1]

C:\Program Files (x86)\Microsoft Visual Studio\Shared\Anaconda3_64\lib\site-packages\pyomo\core\base\util.py in construct(self, data)
123 self._name = base.name
124 self.class = base
--> 125 return base.construct(self, data)
126 construct.doc = base.construct.doc
127 cls.construct = construct

C:\Program Files (x86)\Microsoft Visual Studio\Shared\Anaconda3_64\lib\site-packages\pyomo\core\base\set.py in construct(self, data)
1987 # Bypass the index validation and create the member directly
1988 for index in self.index_set():
-> 1989 self._getitem_when_not_present(index)
1990 finally:
1991 # Restore the original initializer (if overridden by data argument)

C:\Program Files (x86)\Microsoft Visual Studio\Shared\Anaconda3_64\lib\site-packages\pyomo\core\base\set.py in _getitem_when_not_present(self, index)
2030 self._init_values._dimen = _d
2031 try:
-> 2032 _values = self._init_values(_block, index)
2033 except TuplizeError as e:
2034 raise ValueError( str(e) % (

C:\Program Files (x86)\Microsoft Visual Studio\Shared\Anaconda3_64\lib\site-packages\pyomo\core\base\set.py in call(self, parent, index)
412 elif _val is Set.Skip:
413 return _val
--> 414 elif not _val:
415 return _val
416

C:\Program Files (x86)\Microsoft Visual Studio\Shared\Anaconda3_64\lib\site-packages\pandas\core\indexes\base.py in nonzero(self)
2148 def nonzero(self):
2149 raise ValueError(
-> 2150 f"The truth value of a {type(self).name} is ambiguous. "
2151 "Use a.empty, a.bool(), a.item(), a.any() or a.all()."
2152 )

ValueError: The truth value of a MultiIndex is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().`