Fixed GetCompositeScheduleRequest invalid optional access

[alexandrecarrillo]

Describe your changes

Fixed an issue in GetCompositeScheduleRequest command handler.

When the optional field chargingRateUnit is not included in the message request, the handler attempts to read an empty optional value and throws an std::bad_optional_access exception.

OCPP Version

OCPP2.0.1

Describe your solution

When this optional field is missing in the request, the value to use will be the first supported charging rate unit defined in the device model (ChargingScheduleChargingRateUnit).

Otherwise if no valid unit is defined in this variable, the request must be rejected.

Checklist before requesting a review

• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• If OCPP 2.0.1: I have updated the OCPP 2.0.1 status document
• I read the contribution documentation and made sure that my changes meet its requirements