Docstring of Field.get_default is misleading

[tyrion]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Issue

The docstring of Field.get_default says:

If a default has not been set for this field then this will simply
return empty, indicating that no value should be set in the
validated data for this field.

But if default has not been set the method raises SkipField instead.

if self.default is empty or getattr(self.root, 'partial', False):
    # No default, or this is a partial update.
    raise SkipField()

I suggest either to change the documentation to reflect the actual behaviour or change the code to reflect the doc.

https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/fields.py#L434

[tomchristie]

Tweaked the title and description slightly to make it clear it's the method docstring that's incorrect, rather than the documentation.

And yup, good catch - thanks!