Fix flex loading - Githubissues

[x] Appropriate branch selected (all PRs must first be merged to dev before they can be merged to master)
[x] Any modified or new methods or classes have helpful JavaDoc and code is thoroughly commented
[x] The description lists all applicable issues this PR seeks to resolve
[x] The description lists any configuration setting(s) that differ from the default settings
[x] All tests and CI builds passing

This PR seeks to address issues with load flex related items via the UI.

conveyal / gtfs-lib