MySQL and MariaDB have a long list of old, potentially trivial bugs that are annoying if you hit them. No one's really bothered to fix them, so why not you? It doesn't take a large amount of C/C++ knowledge to pick out an old bug and build/test a MySQL/MariaDB patch to fix an old bug.
I'll talk about what is a sane choice of bug, how to use the existing mtr to help, small test cases, and packaging up and submitting your changes.
But doing this, you'll pay it forward, for all the positive MySQL/MariaDB experiences you've had.