Funding

No funding was received for the preparation of this letter.

Conflict of interest

Jufang Song and Rong Zhu have no conflicts of interest that are directly relevant to the content of this article.

Ethics approval

Not applicable.

Consent to participate

Not applicable.

Consent for publication

Not applicable.

Availability of data and material

All data generated or analysed in the preparation of this letter are included in the letter.

Code availability

Not applicable.

Author contributions

JFS participated in the acquisition, analysis or interpretation of the data, and wrote the letter, RZ participated in the acquisition, analysis or interpretation of the data. Both authors have read and approved the final version of the letter, and agree with the order of presentation of the authors.