fix(wallet): Validate currency (#2999)

## Context

This PR is related to 
```
ActiveRecord::NotNullViolation

PG::NotNullViolation: ERROR:  null value in column "balance_currency" of relation "wallets" violates not-null constraint (ActiveRecord::NotNullViolation)
```
The error is raised when creating a wallet with a null currency if the
related customer does not have a currency.

## Description

The PR
- Add a validation on `wallet#currency` making sure it is included in
the accepted currency list.
- Avoid updating the customer currency with a nil value

app/models/wallet.rb

@@ -2,6 +2,7 @@
 
 class Wallet < ApplicationRecord
   include PaperTrailTraceable
+  include Currencies
 
   belongs_to :customer, -> { with_discarded }
 
@@ -15,6 +16,7 @@ class Wallet < ApplicationRecord
   monetize :ongoing_balance_cents, :ongoing_usage_balance_cents, with_model_currency: :balance_currency
 
   validates :rate_amount, numericality: {greater_than: 0}
+  validates :currency, inclusion: {in: currency_list}
 
   STATUSES = [
     :active,

app/services/wallets/create_service.rb

@@ -25,9 +25,9 @@ def call
       wallet = Wallet.new(attributes)
 
       ActiveRecord::Base.transaction do
-        Customers::UpdateCurrencyService
-          .call(customer: result.current_customer, currency: params[:currency])
-          .raise_if_error!
+        if params[:currency].present?
+          Customers::UpdateCurrencyService.call!(customer: result.current_customer, currency: params[:currency])
+        end
 
         wallet.currency = wallet.customer.currency
         wallet.save!

spec/services/wallets/create_service_spec.rb

@@ -93,6 +93,26 @@
         service_result
         expect(customer.reload.currency).to eq('EUR')
       end
+
+      context 'when no currency is provided' do
+        let(:params) do
+          {
+            name: 'New Wallet',
+            customer:,
+            organization_id: organization.id,
+            currency: nil,
+            rate_amount: '1.00',
+            expiration_at:,
+            paid_credits:,
+            granted_credits:
+          }
+        end
+
+        it 'returns an error' do
+          expect(service_result).not_to be_success
+          expect(service_result.error.messages[:currency]).to eq(['value_is_invalid'])
+        end
+      end
     end
 
     context 'when wallet have transaction metadata' do