fix(2.2.1): make optional Session/ChargingPeriod fields omittable

Several "X | None" fields had no default, so they were required-but-nullable —
a counterparty (SMATRICS) that omits them entirely got a 422. Add `= None`
defaults to ChargingPeriod.tariff_id and Session.end_date_time /
authorization_reference / meter_id / total_cost so omitting them is accepted.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 2 people

ocpi/modules/cdrs/v_2_2_1/schemas.py

@@ -50,7 +50,9 @@ class ChargingPeriod(BaseModel):
 
     start_date_time: DateTime
     dimensions: list[CdrDimension]
-    tariff_id: CiString(36) | None  # type: ignore
+    # Optional per spec: allow it to be omitted entirely (not just null), so a CPO
+    # that doesn't send tariff_id doesn't trigger a 422.
+    tariff_id: CiString(36) | None = None  # type: ignore
 
 
 class CdrToken(BaseModel):

ocpi/modules/sessions/v_2_2_1/schemas.py

@@ -15,18 +15,18 @@ class Session(BaseModel):
     party_id: CiString(3)  # type: ignore
     id: CiString(36)  # type: ignore
     start_date_time: DateTime
-    end_date_time: DateTime | None
+    end_date_time: DateTime | None = None
     kwh: Number
     cdr_token: CdrToken
     auth_method: AuthMethod
-    authorization_reference: CiString(36) | None  # type: ignore
+    authorization_reference: CiString(36) | None = None  # type: ignore
     location_id: CiString(36)  # type: ignore
     evse_uid: CiString(36)  # type: ignore
     connector_id: CiString(36)  # type: ignore
-    meter_id: String(255) | None  # type: ignore
+    meter_id: String(255) | None = None  # type: ignore
     currency: String(3)  # type: ignore
     charging_periods: list[ChargingPeriod] = []
-    total_cost: Price | None
+    total_cost: Price | None = None
     status: SessionStatus
     last_updated: DateTime