docs: @NonNull
      public static SourceParams createMultibancoParams(
              @IntRange(from = 0) long amount,
              @NonNull String returnUrl,
              @NonNull String email) {
          return new SourceParams()
                  .setType(Source.MULTIBANCO)
                  .setCurrency(Source.EURO)
                  .setAmount(amount)
                  .setRedirect(createSimpleMap(FIELD_RETURN_URL, returnUrl))
                  .setOwner(createSimpleMap(FIELD_EMAIL, email));
      }