Tensorfow GATHER operator

template <typename InputT, typename PositionsT>
TfLiteStatus Gather(TfLiteContext* context, const TfLiteGatherParams& params,
const TfLiteTensor* input, const TfLiteTensor* positions,
TfLiteTensor* output) {
const PositionsT* indexes = GetTensorData(positions);
bool indices_has_only_positive_elements = true;
const size_t num_indices = positions->bytes / sizeof(PositionsT);
for (size_t i = 0; i < num_indices; i++) {
if (indexes[i] < 0) {
indices_has_only_positive_elements = false;
TF_LITE_ENSURE(context, indices_has_only_positive_elements);

according to this code, I want to know when does indices_has_only_positive_elements become false