Issue in 2019.3 with Python tool as first tool in workflow

A custom tool I'm developing has an optional input defined in the XML file, so that the user could override the data that would normally come from that input connector using the HTML inputs. However, running the workflow with this custom tool as the 'first' tool in a data stream causes the debug workflow to end without processing the python main.py.
As you can see from the image, the first `inv debug` run completes even though there is a `pdb.set_trace()` in the code, and the `"ToolId ..."` output is missing.
The second `inv debug` run is after I updated the debug workflow to include an Text Input tool before the custom tool, and you can see that it stops at the trace point and allows me to inspect the code objects to confirm behavior is as expected.
To create this test tool, I simply copied the `ExampleBatchTool` into a new tool, renamed all the files, updated the places where the name is referenced in the code, and created a simple debug workflow. I've attached a ZIP of the YDMD and YXI files.

[TestOptionalInput.zip](https://github.com/alteryx/snakeplane/files/3752707/TestOptionalInput.zip)