BUG: Dataframe constructor when given dict with None value
- [x] closes #14381
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/14392?src=pr) is 85.26% (diff: 100%)

> No coverage report found for **master** at 096d886.
> 
> Powered by [Codecov](https://codecov.io?src=pr). Last update [096d886...231c2e4](https://codecov.io/gh/pandas-dev/pandas/compare/096d8866a90c8cbb44ab8243320e811fc24190bd...231c2e486182a8c65e14a4ee86eb7bdf39720c75?src=pr)
 @brandonmburroughs Do you have time to update this PR according to the discussion in #14381 (so keep as None)
 @jorisvandenbossche Yes, I'll update based upon the discussion and push the changes in the next day or so.
 @brandonmburroughs Thanks a lot!
