docs: public void retrieveCurrentCustomer(@NonNull CustomerRetrievalListener listener) {
          final Customer cachedCustomer = getCachedCustomer();
          if (cachedCustomer != null) {
              listener.onCustomerRetrieved(cachedCustomer);
          } else {
              mCustomer = null;
  
              final String operationId = UUID.randomUUID().toString();
              mCustomerRetrievalListeners.put(operationId, listener);
              mEphemeralKeyManager.retrieveEphemeralKey(operationId, null, null);
          }
      }