BUG: Constructing DataFrame from list of series with MultiIndex, if MultiIndex contains (NaN, NaN)
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

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

---

I have observed a few issues, when constructing a dataframe from a list of series with multiindices, if any multiindex contains (NaN, NaN).

#### Code Sample, a copy-pastable example

1. In this case I would expect the columns of the dataframe to be the union of the indices of series1 and series2, but ("a", "b") is missing.
```python
import pandas as pd
series1 = pd.Series((1,), index=pd.MultiIndex.from_tuples(((None, None),)))
series2 = pd.Series((10, 20), index=pd.MultiIndex.from_tuples(((None, None), ("a", "b"))))
df = pd.DataFrame([series1, series2])
#   NaN
#   NaN
# 0   1
# 1  10
```

2. There is another issue, when series1 and series2 are flipped.  The columns appear to be correct, but in this case I would expect the value NaN at index 1, column (a,b)):
```python
df = pd.DataFrame([series2, series1])
#     a NaN
#     b NaN
# 0  20  10
# 1   1   1
```

#### Problem description

#### Expected Output
```python
df = pd.DataFrame([series1, series2])
#     a NaN
#     b NaN
# 0  NaN 1
# 1  20  10
```

and the reverse case

```python
df = pd.DataFrame([series2, series1])
#     a NaN
#     b NaN
# 0  20  10
# 1  NaN 1
```


This behavior is not limited to both series containing the MultiIndex (NaN, NaN).  Here is an example, where only one series is constructed with (None, None).  The column ("a", "b") is missing.

```python
import pandas as pd
series1 = pd.Series((1,), index=pd.MultiIndex.from_tuples((("a", None),)))
series2 = pd.Series((10, 20), index=pd.MultiIndex.from_tuples(((None, None), ("a", "b"))))
df = pd.DataFrame([series1, series2])
#      a   NaN
#    NaN   NaN
# 0  1.0   NaN
# 1  NaN  10.0
```


#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : f346574c8bb8921664f6d47d2e4b0f1252e181b9
python           : 3.9.6.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.10.59-1-MANJARO
Version          : #1 SMP PREEMPT Sun Aug 15 13:11:32 UTC 2021
machine          : x86_64
processor        : 
byteorder        : little
LC_ALL           : None
LANG             : en_US.utf8
LOCALE           : en_US.UTF-8

pandas           : 0+untagged.1.gf346574
numpy            : 1.21.1
pytz             : 2021.1
dateutil         : 2.8.2
pip              : 21.1.3
setuptools       : 57.4.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : 7.26.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.4.3
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None

</details>
