Mutable default values for arguments

[max-moser]

Package version (if known): 1.0.0

Describe the bug

It looks like there's some mutable objects used as default values for some function arguments, e.g. a dictionary literal here.
Chances are that this is unintentional and basically a pitfall that I think every Python programmer has fallen into at some point.

Unless this is intended, we should change the default values for arguments to something non-mutable.

[ntarocco]

My findings:

• https://github.com/inveniosoftware/invenio-oauthclient/blob/master/invenio_oauthclient/utils.py#L171
• https://github.com/inveniosoftware/invenio-pages/blob/master/invenio_pages/services/service.py#L52
• https://github.com/inveniosoftware/invenio-rdm-records/blob/master/invenio_rdm_records/oaiserver/services/services.py#L38
• https://github.com/inveniosoftware/flask-resources/blob/master/flask_resources/resources.py#L31
• https://github.com/inveniosoftware/flask-resources/blob/master/flask_resources/serializers/base.py#L48

[max-moser]

Thanks a lot! 👌

[ppanero]

merged flask-resources, re-opening for the rest