fix: process.ForEach JSON selection

[shellcromancer]

Description

The ForEach JSON processor when used with the default jsonnet helpers pass an empty value for the inner processors input_key, this resulted in inner processor having a selection with a trailing . such as processor_type.. This fixes the issue by explicitly handling empty strings when checking the input/output keys.

Motivation and Context

• Fixes usage of the for_each processor when used via jsonnet configurations.

How Has This Been Tested?

This has been tested with the regression suite, and locally by using configuring a processor via jsonnet as follows and getting the expected result, whereas before this no input would be captured from the input array.

// input: {"input_key": ["fizz", "buzz"]}
processlib.for_each('input_key', 'output_key', processlib.capture('', '', '(.*)'))

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.