Klever

Removing tmp vars tries to remove edge with warning tag:
Raise exception:
Traceback (most recent call last):
File "/home/debian/klever-inst/klever/core/core/components.py", line 428, in run
self.main()
File "/home/debian/klever-inst/klever/core/core/components.py", line 332, in callbacks_caller
ret = attr(*args, **kwargs)
File "/home/debian/klever-inst/klever/core/core/vrp/__init__.py", line 246, in fetcher
raise self.__exception
File "/home/debian/klever-inst/klever/core/core/vrp/__init__.py", line 358, in process_single_verdict
get_error_trace_id=True)
File "/home/debian/klever-inst/klever/core/core/components.py", line 332, in callbacks_caller
ret = attr(*args, **kwargs)
File "/home/debian/klever-inst/klever/core/core/vrp/__init__.py", line 259, in process_witness
error_trace = import_error_trace(self.logger, witness)
File "/home/debian/klever-inst/klever/core/core/vrp/et/__init__.py", line 33, in import_error_trace
generic_simplifications(logger, trace)
File "/home/debian/klever-inst/klever/core/core/vrp/et/tmpvars.py", line 23, in generic_simplifications
_basic_simplification(logger, trace)
File "/home/debian/klever-inst/klever/core/core/vrp/et/tmpvars.py", line 35, in _basic_simplification
error_trace.remove_edge_and_target_node(edge)
File "/home/debian/klever-inst/klever/core/core/vrp/et/error_trace.py", line 228, in remove_edge_and_target_node
raise ValueError('Cannot delete edge with warning: {!r}'.format(edge['source']))
KeyError: 'source'