In #125, we added support for using `dist` with sourcemaps, however, we return `null` when not specified and that gets converted into the string `"null"` down the pipeline which has broken the sourcemaps for various customers in the last two weeks.
Also, ss indicated in #138, `dist` is optional for sourcemaps when used with the CLI. Updating the README.me to handle it.
This also removes a warning which shows when the action is run:
```
Warning: Unexpected input(s) 'dist', valid inputs are ['entryPoint', 'args', 'environment', 'sourcemaps', 'finalize', 'ignore_missing', 'ignore_empty', 'started_at', 'version', 'version_prefix',
'set_commits', 'projects', 'url_prefix', 'strip_common_prefix', 'working_directory']
```