Description of problem:

The Start Pipeline Modal does not respect an empty string ('') as a valid default although it is upstream. The UI should not make it a required field in the modal.

Version-Release number of selected component (if applicable):


How reproducible:
Always (create via YAML or CLI)


Steps to Reproduce:
1. Create a Pipeline with an empty string default value (see additional info for suggestions how to do it in the UI)
2. Using the actions (or "more options" menu on the list page) select "Start Pipeline"
3. Try to submit with a empty string default param without touching the field

Actual results:
We show * next to the parameters that don't have defaults. An empty string ('') is a falsy value and thus got confused as a no default provided. This is not valid upstream and needs to change.

Expected results:
Should be able to submit without updating any params that have defaults of an empty string ('').


Additional info:
The Pipeline Builder currently doesn't support this and our UI does not allow for empty strings. Will need UX to fix that portion, but the work around would be to use the Pipeline Builder entirely and then flip over to the YAML to set the default of a param to '' and then create via YAML.