Without the change `gemType` gets defined via `null` attrset that
exposes unevaluatable attribute:
nix-repl> ronin.gemType
error:
… while evaluating the attribute 'gemType'
at pkgs/development/ruby-modules/bundled-common/default.nix:122:30:
121| inherit ruby bundler gems confFiles envPaths;
122| inherit (gems.${pname}) gemType;
| ^
123|
… while evaluating an attribute name
error: value is null while a string was expected
After the change `passthru` does not expose a `gemType` if `pname` is
`null`.
38b39dd404