TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

[Brett C.]

For Bourne-style shells (BASH, ZSH, etc.) ``export CC=gcc`` will do it
for the current shell (won't save it for future use, that requires
setting it in your shell's config file.  For CSH style I think it is
``setenv CC gcc`` but  I am not sure.