install stops when time zone TZ is empty

[tobigithub]

Fresh install on Win64 and R version 4.0.3 (2020-10-10) -- "Bunny-Wunnies Freak Out"
Copyright (C) 2020 The R Foundation for Statistical Computing
Platform: x86_64-w64-mingw32/x64 (64-bit)

> library(rJava)
> .jinit()
> devtools::install_github("Paolobnn/Retiplib")
Downloading GitHub repo Paolobnn/Retiplib@HEAD
  
√  checking for file 'C:\Users\rj\AppData\Local\Temp\RtmpSgSOXC\remotes112061e521a3\PaoloBnn-Retiplib-49bd5fe/DESCRIPTION'

-  preparing 'Retiplib': (626ms)
   checking DESCRIPTION meta-information ...
   checking DESCRIPTION meta-information ... 
√  checking DESCRIPTION meta-information
Warning in as.POSIXlt.POSIXct(x, tz) :
   Warning in as.POSIXlt.POSIXct(x, tz) :
     unable to identify current timezone 'C':
   please set environment variable 'TZ'
-  checking for LF line-endings in source and make files and shell scripts
-  checking for empty or unneeded directories
-  building 'Retiplib_0.2.1.tar.gz'

Error in strptime(xx, f, tz = tz) : 
  (converted from warning) unable to identify current timezone 'C':
please set environment variable 'TZ'
Error: Failed to install 'Retiplib' from GitHub:
  (converted from warning) installation of package ‘C:/Users/rj/AppData/Local/Temp/RtmpSgSOXC/file11203ea06479/Retiplib_0.2.1.tar.gz’ had non-zero exit status
> 

Potential solution: Define timezone or fix and request setting of time zone.
check timezone before:

Sys.timezone()
[1] "unknown"
Warning message:
In Sys.timezone() : unable to identify current timezone 'C':
please set environment variable 'TZ'

> Sys.setenv(TZ='GMT')
> Sys.timezone()
[1] "GMT"