Exception: 'Series' objects are mutable, thus they cannot be hashed
#### Problem

I am trying to explore the **[GDELT](https://blog.gdeltproject.org/gdelt-2-0-our-global-world-in-realtime/)** dataset. I read the file as a csv, having downloaded it from the website. Their initial csv file does not contain the header, but I *added them from the Google Big Query col names*. The header is correct, that I have confirmed multiple times, well, at least it containts the exact amount of columns it should.

When trying to search for any row given a column value, the program crashes with:

> 'Series' objects are mutable, thus they cannot be hashed


#### MInimal Running Example
```
import pandas as pd

python
csv_file_path = "C:\\Users\\and_s\\Downloads\\20181015143000.export.CSV\\20181015143000.export.CSV"

gdelt_data = pd.read_csv(csv_file_path, sep='\t', lineterminator="\n")
gdelt_data = gdelt_data.loc(gdelt_data['actor1_country_code'] == "ITA")
print(gdelt_data)
```

Is this a bug? Because AFAIK strings are hashable.

Also this doesn't work even if I remove null values, so that's not the problem.

