MAC OS: sum over empy series with object dtype gives False 
#### Code Sample, a copy-pastable example if possible

```python
import pandas
pandas.Series(dtype='O').sum()
```

#### Problem description

Performing the above code segment with pandas 0.24.2 gives me 
- (numpy.bool_) `False` on a Mac with homebrew python 3.6.4
- (int) `0` on a Windows 10 with Anaconda python 3.6.7

While I would prefer `0` for my own purposes, I suppose it is not easy to decide on an expected output here. But I would argue that it should at least be consistent.

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

- MAC 
<details>
INSTALLED VERSIONS
------------------

commit: None
python: 3.6.4.final.0
python-bits: 64
OS: Darwin
OS-release: 16.7.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.24.2
pytest: 3.6.2
pip: 19.0.3
setuptools: 39.0.1
Cython: None
numpy: 1.14.2
scipy: 1.0.1
pyarrow: None
xarray: None
IPython: 6.2.1
sphinx: None
patsy: None
dateutil: 2.7.2
pytz: 2018.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 3.0.0
openpyxl: None
xlrd: 1.1.0
xlwt: None
xlsxwriter: None
lxml.etree: 4.2.5
bs4: 4.6.3
html5lib: 0.9999999
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
gcsfs: None
23846nemo/linearization.py000418:1
LinterAtom Ide DiagnosticsActivate Power Mode
Python 3 | idle
CRLFUTF-8PythonGitHubGit (0)4 updates
</details>


- WIN
<details>
INSTALLED VERSIONS
------------------

commit: None
python: 3.6.7.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 78 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.24.2
pytest: 4.0.2
pip: 18.1
setuptools: 40.6.3
Cython: 0.29.2
numpy: 1.15.4
scipy: 1.1.0
pyarrow: None
xarray: None
IPython: 7.2.0
sphinx: 1.8.2
patsy: 0.5.1
dateutil: 2.7.5
pytz: 2018.7
blosc: None
bottleneck: 1.2.1
tables: 3.4.4
numexpr: 2.6.8
feather: None
matplotlib: 3.0.2
openpyxl: 2.5.12
xlrd: 1.2.0
xlwt: 1.3.0
xlsxwriter: 1.1.2
lxml.etree: 4.2.5
bs4: 4.6.3
html5lib: 1.0.1
sqlalchemy: 1.2.15
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
gcsfs: None
47327experiments\pyomo_nl.py50:1
Python 3 | idle
CRLFenUS,deDEUTF-8Python
developmentFetchGitHubGit (45)
</details>
