Added empty dictionary for ComputeError extras default instead of None

[coltonbh]

Description

As per previous discussion about native_files when we have empty fields that are dict objects we want their default value to be {} not None. {} evaluates falsey in python so it can still be treated as a "null object" and we remove needing to check the case of None for .extras. This makes coding easier because we can always do:

compute_error.extras['hi'] = 'new value'

Instead of having to always check this first:

if compute_error.extras is None:
    compute_error.extras = {"hi': 'new value}
else:
    compute_error.extras["hi'] =  'new value

Changelog description

Change default value for ComputeError.extra from None to {}

Status

• [ x] Code base linted
• [ x] Ready to go

[codecov]

Codecov Report

Merging #301 (d00d676) into master (d04a380) will decrease coverage by 0.04%.
The diff coverage is n/a.

Additional details and impacted files

[coltonbh]

I think something might be funny with the Format GitHub action. When I run black locally using python3.7 everything is good.