Allow return statement without arguments

[joente]

Description

Allow the return; statement to be used without arguments to implicitly return nil.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Test syntax updated

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• New and existing unit tests pass locally with my changes