private void ensureUserIdsIsMutable() {
        com.google.protobuf.Internal.LongList tmp = userIds_;
        if (!tmp.isModifiable()) {
            userIds_ = com.google.protobuf.GeneratedMessageLite.mutableCopy(tmp);
        }
    }
<code>repeated int64 user_ids = 1;</code>

@param index The index of the element to return.
@return The userIds at the given index.
turms-client-kotlin/src/main/java/im/turms/client/model/proto/request/user/relationship/QueryRelationshipsRequest.java