[Bug]: A primitive bound to a combo list does not select the first item when null

### Frontend Version

1.3.26

### Expected Behavior

A primitive attached to a combo list (e.g. Load Image's image input) with its widget value set to null should select the first item in the list on load.

### Actual Behavior

A primitive attached to a combo list (e.g. Load Image's image input) with its widget value set to null keeps the value as null. This:
1. causes the workflow to fail with an error when run;
2. requires you to click on the primitive to update its value.

### Steps to Reproduce

1. Add a "Load Image" node (or other loader such as the "Load LoRA" node).
2. Make the input file list an input instead of a widget.
3. Connect the input node from (2) to a primitive node -- this will show the file list in the dropdown.
4. Complete the workflow, e.g. by attaching the "Load Image" output to a "Preview Image" node.
5. Run the workflow ensuring there are no errors.
6. Save/export the workflow.
7. Edit the workflow file so the primitive widget value is null for the filename.
8. Reimport the workflow.
9. Run the workflow.

### Debug Logs

```powershell
n/a
```

### Browser Logs

n/a

### Setting JSON

```json
{
"Comfy.NodeLibrary.Bookmarks": [],
"Comfy.LinkRenderMode": 2,
"Comfy.UseNewMenu": "Top",
"Comfy.ColorPalette": "dark",
"Comfy.DevMode": true,
"Comfy.Settings.ExtensionPanel": false,
"pysssss.SnapToGrid": true
}
```

### What browsers do you use to access the UI ?

Mozilla Firefox

### Other

This is the behaviour for Load Image when its input is null. Possibly other load nodes as well.

Use Case: Separate the selection of a LoRA filename from the loading of the LoRA. Remove file path information from the workflow that will be different for each user.