Arvados

The docker/build_tools/config.rb script substitutes the string @_NOT_FOUND_@ for any configuration variable required that isn't found in config.yml.

It's an ugly hack that causes some confusing downstream problems: for example, if this string appears as the value of a field in application.yml, it produces this error when trying to build the API server image:

rake aborted!
Psych::SyntaxError: (<unknown>): found character that cannot start any token while scanning for the next token at line 53 column 22
/usr/src/arvados/services/api/config/initializers/zz_load_config.rb:7:in `block in <top (required)>'

A better solution would be to raise an exception, forcing the user to correct the problem immediately at config time. Alternatively, substitute a syntactically valid string like VARIABLE_NOT_FOUND which can be parsed, but is at least likely to appear in error messages in a way that will make it easier to trace to their source.