Filled area in scatterplot does not honor null values

Opening a new issue as requested here: https://github.com/plotly/plotly.js/issues/1132

When the scatter plot has null values on the y axis, the line drawn by plotly.js is disconnected over this area as expected. However, with fill: 'tozeroy', the filled area still spans the area with null values instead going only from known values to zero.

Short example, can be seen here: https://www.fi.muni.cz/~kas/plots/plotly-issue-7448.html

Plotly.newPlot('somediv', [{
  type: "scatter",
  mode: "lines",
  x: [1,2,3,4,5],
  y: [1,2,null,2,1],
  fill: 'tozeroy',
}]);

In this example, there is no line drawn beetween (x=2, y=2) and (x=4, y=2) points as expected. There should be no filled area between x = 2 and x = 4 as well.

Thanks!

Inizia dalla riproduzione fornita di Plotly.newPlot e traccia la gestione del riempimento del grafico a dispersione per i valori y null. La correzione è completa quando fill: 'tozeroy' lascia non riempito l'intervallo tra x=2 e x=4, preservando al contempo il comportamento previsto della linea disconnessa.