Plotly generates many warnings because of trying to set `structure(NULL)`

This line in plotly:
https://github.com/ropensci/plotly/blob/a76100d7c06774ec50c07982ff6bfdb6d2d09e2d/R/plotly_build.R#L281-L284

can result in setting structure(NULL), which throws many warnings.

I have an app with many plots, and one plot generates dozens of copies of this warning:

Warning in structure(if (i %in% npscales()) uniq(d[[i]]) else d[[i]], class = oldClass(x[[i]])) : Calling 'structure(NULL, *)' is deprecated, as NULL cannot have attributes. Consider 'structure(list(), *)' instead.

I don't have a minimal reprex because I haven't spent too much time finding out what kind of data can cause a NULL there, but it's definitely a NULL in d[[i]] that causes these warnings.

Commencez dans R/plotly_build.R aux lignes 281-284 et suivez comment une valeur NULL dans d[[i]] atteint structure(). Reproduisez l’avertissement avec un graphique contenant la forme de données concernée, puis vérifiez que plotly n’émet plus les avertissements de dépréciation répétés tout en préservant le comportement existant de construction du graphique.