add ability to hide missing data from hover tooltip

I have a dataframe column with some missing values which I want to include in hover_data. Is it possible to show the column in the hover tooltip only if there's value for the currently hovered point? The current default behavior is to show col_name=%{customdata[0]} for missing values. I think it would be better to show nothing at all.

import plotly.express as px

df = px.data.gapminder().query("continent=='Oceania'")

df["pop"] = None

fig = px.line(
    df,
    x="year",
    y="lifeExp",
    color="country",
    hover_data=["pop"],
    title="layout.hovermode='closest' (the default)",
)
fig.update_traces(mode="markers+lines")

fig.show()

Start by reproducing the provided Python example with plotly.express.line and hover_data, then trace how missing values become hover tooltip text. Done means points with missing values no longer display the hover column, while populated values remain visible; add or update coverage for this behavior if the relevant test area is found.