Refactoring: proper handling of filepath.Glob errors

In several places we use the `filepath.Glob` function that can return an error if the glob expression is invalid. We do not always properly handle this error. 

There are two options of how to approach this:

1. Catch the error where the `filepath.Glob` function is used and return it to the caller scope.
2. Validate glob expressions somewhere closer to the top of the call stack.