Fixed #20658 -- Fixed bad reST formatting and missing parentheses in the docs for CBV mixins

Thanks to Keryn Knight for the report.
Fixed #20462 -- null/non-string regex lookups are now consistent

Thanks to noirbizarre for the report and initial patch.
Fixed #20462 - Replaced the str() cast introduced in 273dc55 by force_text()
Merge pull request #1308 from loic/ticket20462

Fixed #20462 - Replaced the str() cast introduced in 273dc55 by force_text()