string prefix_cmp;
    const char* child_scope_name;
    if (prefix == nullptr) {
      child_scope_name = "gradients";
    } else {
      prefix_cmp = string(prefix) + "/";
      // The operation should fail if the provided name prefix has already been
      // used in this graph
      for (const auto& pair : g->name_map) {
        const string& name = pair.first;