fix: proper return values to become lint clean

Author: mnezerka

pyodata/v2/model.py

@@ -1018,6 +1018,8 @@ def association(self, association_name, namespace=None):
             except KeyError:
                 pass
 
+        raise KeyError('Association does not exist')
+
     @property
     def associations(self):
         return list(itertools.chain(*(decl.list_associations() for decl in list(self._decls.values()))))
@@ -1048,6 +1050,8 @@ def association_set(self, set_name, namespace=None):
             except KeyError:
                 pass
 
+        raise KeyError('Association set does not exist')
+
     @property
     def association_sets(self):
         return list(itertools.chain(*(decl.list_association_sets() for decl in list(self._decls.values()))))