no
doesn’t become false
, it becomes Norway
, and when converted to a boolean, Norway is true. The reason’s because one on YAML’s native types is an ISO country code enum, and if you tell a compliant YAML implementation to load a file without giving it a schema, that type has higher priority than string. If you then call a function that converts from native type to string, it expands the country code to the country name, and a function that coerces to boolean makes country codes true.
The problem’s easy to avoid, though. You can just specify a schema, or use a function that grabs a string/bool directly instead of going via the assumed type first.
The real problem with YAML is how many implementations are a long way from being conformant, and load things differently to each other, but that situation’s been improving.
You’re allowed to charge before you give access to the software, but then can’t restrict the people you give it to giving it to more people. The beer licence sounds like those people would be on the hook for beer, too.