Fix types in holders

Author: bonjourmauko

openfisca_core/holders/holder.py

@@ -117,7 +117,7 @@ def get_memory_usage(self) -> MemoryUsage:
             >>> entity = entities.Entity("", "", "", "")
 
             >>> class MyVariable(variables.Variable):
-            ...     definition_period = "year"
+            ...     definition_period = periods.DateUnit.YEAR
             ...     entity = entity
             ...     value_type = int
 
@@ -188,7 +188,7 @@ def set_input(
             >>> entity = entities.Entity("", "", "", "")
 
             >>> class MyVariable(variables.Variable):
-            ...     definition_period = "year"
+            ...     definition_period = periods.DateUnit.YEAR
             ...     entity = entity
             ...     value_type = int
 

openfisca_core/holders/tests/__init__.py

@@ -250,7 +250,9 @@ def _raise_error(value: str) -> NoReturn:
     Examples:
         >>> _raise_error("Oi mate!")
         Traceback (most recent call last):
-        ValueError: Expected a period (eg. '2017', ...); got: 'Oi mate!'.
+        ValueError: Expected a period (eg. '2017', '2017-01', '2017-01-01', ...
+        Learn more about legal period formats in OpenFisca:
+        <https://openfisca.org/doc/coding-the-legislation/35_periods.html#pe...
 
     """
 

openfisca_core/periods/helpers.py

@@ -246,7 +246,7 @@ def date(self) -> "Date":
             >>> period = Period((DateUnit.YEAR, instant, 3))
             >>> period.date
             Traceback (most recent call last):
-            ValueError: "date" is undefined for a period of size > 1: year:2021-09:3.
+            ValueError: "date" is undefined for a period of size > 1: year:2021-10:3.
 
         """
 

openfisca_core/periods/period_.py

@@ -397,7 +397,7 @@ def get_parameters_at_instant(
 
         """
 
-        key: Instant
+        key: Optional[Instant]
         msg: str
 
         if isinstance(instant, Instant):

openfisca_core/taxbenefitsystems/tax_benefit_system.py

@@ -326,6 +326,8 @@ def get_formula(
 
         """
 
+        instant: Optional[Instant]
+
         if not self.formulas:
             return None
 
@@ -340,6 +342,9 @@ def get_formula(
             except ValueError:
                 instant = periods.instant(period)
 
+        if instant is None:
+            return None
+
         if self.end and instant.date > self.end:
             return None