Registrations for groups with value 0 crash the group's page

[hugocorbucci]

This happened for group 81 for event 20 (Agile Brazil 2016).
The group was created as a value 0 group without a discount field entered.
Once attendances were added, the group page was failing because the total_price could not be calculated as attendances had registration_value as nil.

We worked around it by manually setting the value to 0 and changing the group to have 100% discount but there is something there to fix.

[sampatbadhe]

@hugocorbucci I can help you on this.

Is default value for registration_value is 0?

[hugocorbucci]

Hey @sampatbadhe thanks for volunteering :)
So, registration_groups can have a specified value amount (registration_group.amount). In which case, the registration_value for an attendance in that group should be exactly that amount.
If a group is created with an amount 0, then the registration_value for any attendance in that group should be 0. Does that make sense?