I have no idea what am doing wrong. The last test always fails, but
I think my solution managed to update the both version (the string and the symbol as well).
I use p method to inspect the self:

• before the update: {:enabled=>nil, "enabled"=>true}
• after the update: {:enabled=>false, "enabled"=>false}

That seems just right to me, but the test constantly fails:

Test Failed: Should update key :enabled even if it's 'nil'