Fix #21356: JSON nested_to_record Silently Drops Top-Level None Values
- [x] closes #21356 
- [x] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

@WillAyd Kindly review, this is my first PR to pandas! # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21363?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@636dd01`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21363/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21363?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #21363   +/-   ##
=========================================
  Coverage          ?   91.85%           
=========================================
  Files             ?      153           
  Lines             ?    49562           
  Branches          ?        0           
=========================================
  Hits              ?    45525           
  Misses            ?     4037           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.25% <ø> (?)` | |
| #single | `41.86% <ø> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21363?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/json/normalize.py](https://codecov.io/gh/pandas-dev/pandas/pull/21363/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vbm9ybWFsaXplLnB5) | `96.87% <ø> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21363?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21363?src=pr&el=footer). Last update [636dd01...b7bda86](https://codecov.io/gh/pandas-dev/pandas/pull/21363?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @WillAyd if you have a few, can you rebase this @jreback think its good to go. First time doing that so let me know if anything looks off @daminisatya Thanks a lot!