[Bug]: SpatialSeries.reference_frame should be optional

[rly]

What happened?

The spec for SpatialSeries says that the "reference_frame" dataset is optional. However, it is a required argument in pynwb to the SpatialSeries constructor.

This is blocking a user from validating their NWB files for upload onto DANDI after creating them using MatNWB.

Steps to Reproduce

n/a

Traceback

No response

Operating System

Windows

Python Executable

Conda

Python Version

3.11

Package Versions

No response

Code of Conduct

• [X] I agree to follow this project's Code of Conduct
• [X] Have you checked the Contributing document?
• [X] Have you ensured this bug was not already reported?

[rly]

The situation is odd though - the constructor for SpatialSeries should not be called during validation. Only builders are needed. The error is: ConstructError: Could not construct SpatialSeries object due to: SpatialSeries.__init__: missing argument 'reference_frame'

[rly]

Never mind the last comment. NWB inspector reads the file and therefore the objects are constructed.