For the most part, yes, it’s not safe to walk through some parts of Abuja at night alone. Worse if you are a woman. It’s smart, however, to adhere to some common sense principles that are valid for any urban environment:
Avoid empty streets when walking alone
Avoid areas that seem clearly derelict
Give the appearance that you have a destination and know where you’re going. There are exceptions to this, such as strolling through a known tourist destination, but most of that isn’t done at night.
Stay in well-lit areas.
Don’t wander off into unfamiliar areas unnecessarily.
Keep expensive items and other items worth stealing out of sight as much as possible.
Don’t get incredibly inebriated on your own and then plan to walk somewhere on your own at night.
Don’t intercede when strangers are having a dispute. It could be a scam, set up to rob you.