Different output for get_maintainer and get_authors when Authors@R field malformed

[maciekbanas]

First of all - thank you for the package. It does the job!

This issue is not critical, but I would prefer same output, when developer fills DESCRIPTION by hand and fails to write properly Authors@R field, e.g. forgets about last bracket ). For the time-being get_maintainer in that case returns character "NULL" which is awkward, while get_authors returns classic NULL.

Reprex below:

> desc_malformed_authors <- 
+   paste0("Package: TestPackage\nTitle: Test package\nVersion: 0.0.0.9000\n",
+          "Authors@R: \n    c(person(given = \"John\", family = \"Test\", \n ",
+          "email = \"john.test@tests.com\", \n role = c(\"aut\", \"cre\")),\n ",
+          "person(given = \"Joanna\", family = \"Checks\", \n ", 
+          "email = \"joanna.checks@tests.com\", \n role = c(\"aut\"))\n",
+          "Description: This package aims to test\n")
> desc_env <- desc::desc(text = desc_malformed_authors)
> desc_env
Package: TestPackage
Title: Test package
Version: 0.0.0.9000
Authors@R (parsed):
    * NULL
Description: This package aims to test
> desc_env$get_maintainer()
[1] "NULL"
> desc_env$get_authors()
NULL