BUG: pandas.DataFrame.reindex -  sample code to expand the dataframe as given in the API reference is not working
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- [x ] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---


#### Code Sample, a copy-pastable example
date_index = pd.date_range('1/1/2010', periods=6, freq='D')
df2 = pd.DataFrame({"prices": [100, 101, np.nan, 100, 89, 88]},
                   index=date_index)
df2
date_index2 = pd.date_range('12/29/2009', periods=10, freq='D')
df2.reindex(date_index2)
df2

```python
date_index = pd.date_range('1/1/2010', periods=6, freq='D')
df2 = pd.DataFrame({"prices": [100, 101, np.nan, 100, 89, 88]},
                   index=date_index)
df2
date_index2 = pd.date_range('12/29/2009', periods=10, freq='D')
df2.reindex(date_index2)
df2
```

#### Problem description

Unable to expand a dataframe using reindex, if the index is datetime. It works for other data types. The code is copied from the  [API reference](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.reindex.html) of Pandas
#### Expected Output
            prices
2009-12-29     NaN
2009-12-30     NaN
2009-12-31     NaN
2010-01-01   100.0
2010-01-02   101.0
2010-01-03     NaN
2010-01-04   100.0
2010-01-05    89.0
2010-01-06    88.0
2010-01-07     NaN
#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : 5f648bf1706dd75a9ca0d29f26eadfbb595fe52b
python           : 3.9.6.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
Version          : 10.0.19043
machine          : AMD64
processor        : Intel64 Family 6 Model 61 Stepping 4, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : English_India.1252

pandas           : 1.3.2
numpy            : 1.21.1
</details>
