BUG: read_parquet unexpected output with pyarrow 0.16.0 and nullable usigned int dtype
```python
data = [np.nan, 1, 2, 3, 4]
df = pd.DataFrame()
df['col'] = pd.Series(data, dtype = "UInt32")
df.to_parquet('example.parquet')
res = pd.read_parquet('example.parquet')
print(res)
```
#### Problem description

The above cope prints:
```
    col
0  <NA>
1     0
2     1
3     0
4     2
```

This happened after I upgraded to `pyarrow 0.16.0`, and `UInt32` is the only dtype that I had trouble with.
The problem should be with `read_parquet`, I tried reading parquet with another package, and got the expected output.

#### Expected Output
```
    col
0  <NA>
1     1
2     2
3     3
4     4
```
#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.3.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 18.7.0
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.0.1
numpy            : 1.17.3
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 20.0.2
setuptools       : 45.2.0.post20200210
Cython           : None
pytest           : 5.3.2
hypothesis       : None
sphinx           : 2.3.0
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.4.2
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.1
IPython          : 7.11.1
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.4.2
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 0.16.0
pytables         : None
pytest           : 5.3.2
pyxlsb           : None
s3fs             : 0.4.0
scipy            : 1.4.0
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None
numba            : 0.48.0
</details>
