Warning in install.packages : converting NULL pointer to R NULL

install.packages('cowplot',lib=.Rlib) 
trying URL 'https://cloud.r-project.org/src/contrib
/cowplot_1.0.0.tar.gz'
Content type 'application/x-gzip' length 1275585 bytes (1.2 MB)
==================================================
downloaded 1.2 MB

* installing *source* package ?cowplot? ...
** package ?cowplot? successfully unpacked and MD5 sums checked
** using staged installation
** R
** inst
** byte-compile and prepare package for lazy loading
** help
*** installing help indices
*** copying figures
** building package indices
** installing vignettes
** testing if installed package can be loaded from temporary location
** testing if installed package can be loaded from final location
** testing if installed package keeps a record of temporary installation path
* DONE (cowplot)

The downloaded source packages are in
	?/tmp/RtmpG8wb97/downloaded_packages?

sessionInfo()
R version 4.0.0 (2020-04-24)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 18.04.4 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/atlas/libblas.so.3.10.3
LAPACK: /usr/lib/x86_64-linux-gnu/atlas/liblapack.so.3.10.3

Random number generation:
 RNG:     Mersenne-Twister 
 Normal:  Inversion 
 Sample:  Rounding 
 
locale:
 [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_NZ.UTF-8        LC_COLLATE=en_GB.UTF-8    
 [5] LC_MONETARY=en_NZ.UTF-8    LC_MESSAGES=en_GB.UTF-8   
 [7] LC_PAPER=en_NZ.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_NZ.UTF-8 LC_IDENTIFICATION=C       

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

other attached packages:
[1] brev_0.0-4

loaded via a namespace (and not attached):
[1] compiler_4.0.0 tools_4.0.0