[pyobas] Update mandatory contract properties

Author: guillaumejparis

pyobas/contracts/contract_config.py

@@ -71,9 +71,9 @@ class ContractElement(ABC):
     key: str
     label: str
     type: str = field(default="", init=False)
-    mandatoryGroups: List[str] = None
-    mandatoryConditionField: str = None
-    mandatoryConditionValue: str = None
+    mandatoryGroups: List["ContractElement"] = field(default_factory=list)
+    mandatoryConditionField: List["ContractElement"] = field(default_factory=list)
+    mandatoryConditionValue: List[str] = field(default_factory=list)
     linkedFields: List["ContractElement"] = field(default_factory=list)
     linkedValues: List[str] = field(default_factory=list)
     mandatory: bool = False