It's only a fallback message, in case the parser reports `end-of-file`, but `check-parens` doesn't find an error.  I can't think of a situation where this could occur, but better safe than sorry, and in either case, we must never silently swallow errors.

The “real” error message is reported by `cask-cli--check-parens`, which points to the exact line and column number of the first unbalanced parenthesis.  This information is usually sufficient to find the syntax error, especially in a file as simple as a cask file with at most two levels of nested parenthesis.