Unused color level is dropped in `ggmice()` legend

[hanneoberman]

library(mice)
#> Warning: package 'mice' was built under R version 4.3.1
#> 
#> Attaching package: 'mice'
#> The following object is masked from 'package:stats':
#> 
#>     filter
#> The following objects are masked from 'package:base':
#> 
#>     cbind, rbind
library(ggmice)
#> 
#> Attaching package: 'ggmice'
#> The following objects are masked from 'package:mice':
#> 
#>     bwplot, densityplot, stripplot, xyplot
library(ggplot2)
#> Warning: package 'ggplot2' was built under R version 4.3.3
ggmice(nhanes, aes(bmi)) + geom_histogram(fill = "white")
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.
#> Warning: Removed 9 rows containing non-finite outside the scale range
#> (`stat_bin()`).

萀Ȭ
#> Error in eval(expr, envir, enclos): object '萀Ȭ' not found

^{Created on 2024-03-05 with reprex v2.1.0}