Empty dependency field normalizes to invalid file

[infotroph]

A corner case, seen when bulk-normalizing a directory full of legacy packages: If any dependency field (Depends, Imports, Suggests, Enhances, LinkingTo) is present but empty, normalizing the file leaves an empty line that is treated as an error on rereading.

> library(desc)
> x <- desc("!new")
> x$set("Depends", "")
> x
Package: {{ Package }}
Title: {{ Title }}
Version: 1.0.0
Authors@R (parsed):
    * Jo Doe <jodoe@dom.ain> [aut, cre]
Maintainer: {{ Maintainer }}
Description: {{ Description }}
License: {{ License }}
URL: {{ URL }}
BugReports: {{ BugReports }}
Depends:

Encoding: UTF-8
> x$normalize()
> x
Error in if (R && x$value == "R") return(TRUE) : 
  missing value where TRUE/FALSE needed
> DSC <- tempfile()
> x$write(DSC)
> desc(DSC)
Error: Empty lines found in DESCRIPTION file

Expected behavior

I'd be satisfied if normalize() left these fields in a valid-but-empty state and mildly pleased if by default it removed them with a message, but your call what's correct -- I've seen and noted that ?desc::description says "The format of the various fields is opinionated and you might like it or not" 😄

Session info

> sessionInfo()
R version 4.3.2 (2023-10-31)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Sonoma 14.4.1

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/lib/libRblas.0.dylib 
LAPACK: /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.11.0

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

time zone: America/Los_Angeles
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] desc_1.4.3.9000

loaded via a namespace (and not attached):
[1] compiler_4.3.2 R6_2.5.1       cli_3.6.2      tools_4.3.2