You can always test for nil explicitly. Compare: unless foo # ... foo can be false or nil to reach this branch end unless foo == false # ... thi

You can always test for nil explicitly. Compare: unless foo # ... foo can be false or nil to reach this branch end unless foo == false # ... this branch is reached unless foo == false end Since terseness is considered such a cardinal virtue amongst Ruby programmers (including myself), however, this kind of issue is often ignored, and difficult to detect unless your tests explicitly check for "truthy" and "non-truthy" values in addition to the true/false literals.