private void ensureUnreachableIsMutable() {
      if (!unreachable_.isModifiable()) {
        unreachable_ = new com.google.protobuf.LazyStringArrayList(unreachable_);
      }
      bitField0_ |= 0x00000004;
    }
<pre>
Token to retrieve the next page of results, or empty if there are no more
results in the list.
</pre>

<code>string next_page_token = 2;</code>

@param value The bytes for nextPageToken to set.
@return This builder for chaining.
java-valkey/proto-google-cloud-valkey-v1/src/main/java/com/google/cloud/memorystore/v1/ListBackupCollectionsResponse.java