Reproducing https://github.com/robotframework/ride/issues/1661

lib.py

from robot.libraries.BuiltIn import BuiltIn, register_run_keyword

def my_keyword(thing):
    BuiltIn().run_keyword("Log", thing)

# Uncommenting this also resolves the issue.
# register_run_keyword(__name__, my_keyword)

test.robot

* Settings *
Library    lib.py

* Test Cases *
Should Gracefully Pickle Regex Pattern
    ${Pattern}=    Evaluate    re.compile('w4rsdg')    re
    My Keyword    ${Pattern}