Don't strip empty query params when paginating

[npars]

Description

Fixes issue with pagination when the url contains empty query params. The previous implementation would strip out any empty query params from the next and previous urls. This PR fixes the query parsing and ensures that empty query params are preserved.

This possibly fixes #3328.

[codecov-io]

Current coverage is 91.23%

Merging #4260 into master will not change coverage

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[tomchristie]

The previous implementation would strip out any empty query params from the next and previous urls.

Why is that a problem?
The current behavior as describes sounds more desirable to me on first sight.

Closing for now, but may consider reopening given sufficient cause.

[npars]

The request object received by the View treats empty query params and missing query params differently:

GET http://testserver/?filter=

(Pdb) repr(request.query_params.get('filter'))
"u''"

GET http://testserver/

(Pdb) repr(request.query_params.get('filter'))
'None'

This means that when paginating the next and previous pages could contain a completely different data set from the current query if the API is relying on this behaviour.

We currently have an implementation that uses this behaviour for passing search strings into the API. An empty search string is considered valid and returns different results than when the search param is not provided at all. As a result of this only the first page from DRF is valid, all subsequent pages contain the incorrect dataset.

[tomchristie]

Gotcha - thanks for clarifying.

[tomchristie]

Okeydokes - this looks good to me. Thanks for your work on it! 😄

Closes #4392
Closes #4393