bash null conditional

[Craig White]

I'm in my bash book and looking on web but can't seem to resolve this
simple problem.

$ if [ -n "grep A121 myfile.csv" ]; then echo "null"; fi
null

$ if [ -n "grep A125 myfile.csv" ]; then echo "null"; fi
null

A125 definitely is null when I just run the grep command in the quotes
but A121 definitely is not null.

What am I missing on the if/null operator here?

Craig