ScratchData notes passed as None instead of empty string in add_scratch

[lvsltz]

Description

If an np.ndarray is added in scratch with nwbfile.add_scratch(ndarray,name='some_name') without a notes argument, ScratchData is created with notes = None and fails with
TypeError: ScratchData.__init__: incorrect type for 'notes' (got 'NoneType', expected 'str')

Adding something like this before https://github.com/NeurodataWithoutBorders/pynwb/blob/dev/src/pynwb/file.py#L695 should fix it.

if notes is None:
    notes = ''

Steps to Reproduce

data = np.random.randint(0,30,(5,9))
nwbfile.add_scratch(data, name = 'some_name')

Environment

Python Executable: Conda
Python Version: 3.7
Operating System: Linux
HDMF Version: pynwb 1.3.3, hdmf 1.6.4

Checklist

• Have you ensured the feature or change was not already reported?
• Have you included a brief and descriptive title?
• Have you included a clear description of the problem you are trying to solve?
• Have you included a minimal code snippet that reproduces the issue you are encountering?
• Have you checked our Contributing document?

[bendichter]

Thank, @lvsltz! Looks like Ryan is on this.