[BUG] Internal server error on "validate inputs" if artifact input param has no outputs

[colton-lapp]

Describe the bug
If you have a task graph that references an artifact input parameter with no output parameter, you get an internal server error when you click "validate inputs":

To Reproduce
Steps to reproduce the behavior:

1. Copy the Entrypoint settings in screenshot
2. Click "Validate Inputs"

Expected behavior
This should show a useful notification that the types are incompatible

Screenshots
See above