Add file source. Configure the 'Path Field' to be some field such as 'fileName', but without adding it as a column in the output schema.
Add several other nodes to the pipeline, just to add some arbitrary complexity, and to take it to completion (other sources, transforms, sinks, etc.).
Now, attempt to run a preview of this pipeline.
The user just sees a red bar with the message:
"Path field 'fileName' is not present in the schema. Please add it to the schema as a string field."
From this, it is not clear which node is problematic. This is especially difficult for the user if the user has multiple nodes in the pipeline.
Note that unlike running preview, deploying the pipeline gives a better error message, by including the stage name:
"Failed to configure pipeline: Error configuring stage 'File': Path field 'fileName' is not present in the schema. Please add it to the schema as a string field."