Good day,
I also see NULL on R start-up. I installed R from source.
$ R-4.1.0/bin/R
R version 4.1.0 (2021-05-18) -- "Camp Pontanezen"
... ...
Type 'q()' to quit R.
NULL
I noticed a couple of error messages at the end of the installation which I thought were harmless. I will reinstall R. The extracted directory and prefix directory were the same, which might be problematic.
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Dario Strbenac
University of Sydney
Camperdown NSW 2050
Australia