[Bug]: decorate_grob_set fails when combining empty string and spaces in footnotes

[BFalquet]

What happened?

This is a funny one:

This fails:

x <- chevron::run(chevron::mng01, chevron::syn_data, dataset = "adlb")
x <- lapply(x, ggplot2::ggplotGrob)

res <- tern::decorate_grob_set(
  x,
  titles = "title",
  footnotes = c("", "a a") # empty string and space
)
#> Error in if (grid::convertWidth(linewidth + gapwidth + width_i, grid::unitType(width), : missing value where TRUE/FALSE needed

This works

res <- tern::decorate_grob_set(
  x,
  titles = "title",
  footnotes = c(" ", "a a") # space and space
)

res <- tern::decorate_grob_set(
  x,
  titles = "title",
  footnotes = c("", "axa") # empty string and no space
)

res <- tern::decorate_grob_set(
  x,
  titles = "title",
  footnotes = c(" ", "axa") # blank space and no space
) 

res <- tern::decorate_grob_set(
  x,
  titles = "title",
  footnotes = c("a a", "") # blank space and empty string
)

The only condition where the function fails is when the first element of the vector is empty string and the other contains a blank space.

also when footnotes is NULL, the error is not very user friendly

x <- chevron::run(chevron::mng01, chevron::syn_data, dataset = "adlb")
x <- lapply(x, ggplot2::ggplotGrob)

res <- tern::decorate_grob_set(
  x,
  titles = "title",
  footnotes = NULL
)
#> Error in strsplit(text, " "): non-character argument
Created on 2024-06-18 with [reprex v2.1.0](https://reprex.tidyverse.org/)

Have fun!

sessionInfo()

No response

Relevant log output

> packageVersion("tern")
[1] ‘0.9.4.9009’

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