Key error function find_output with undeclared output parameters

This problem will cause critical failure with OTBTF PatchesExtraction, may be any other app when using in memory.
Steps to reproduce :

• init PatchesExtraction with outputlabels param but skip other source*.out parameters e.g. you want to set parameters type later using .write
  The app will run as intended. Later, the problem will occur when setting the finished attribute : here I added a function to check parameters outputs, my bad :

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Input In [31], in <cell line: 1>()
----> 1 a.execute()

File ~/Code/git/pyotb/pyotb/core.py:616, in App.execute(self)
    613         except RuntimeError:
    614             pass  # this is when there is no value for key
--> 616 return self.finished

File ~/Code/git/pyotb/pyotb/core.py:531, in App.finished(self)
    525 @property
    526 def finished(self):
    527     """
    528     Property to store whether App has been executed
    529     :return: True or False
    530     """
--> 531     if self._finished and self.find_output():
    532         return True
    533     return False

File ~/Code/git/pyotb/pyotb/core.py:628, in App.find_output(self)
    626 missing = []
    627 for param in self.output_parameters_keys:
--> 628     filename = self.parameters[param]
    629     if Path(filename).exists():
    630         files.append(filename)

KeyError: 'source1.out'

So here in output_parameters_keys, we have every available param, but they don't exists in self.parameters

TODO: catch key error, make this more user friendly + enhance .finished and find_outputs()