I have a dataframe contains a tuple of (lat,lon), but there are some row contain a tuple of nan. How can I remove or detect these? 

Example:

```
import pandas as pd
import numpy as np

df = pd.DataFrame(data={'location': [1, 2, 3],
                        'coor': [(14.48847, 103.161477),
                              (14.970084, 103.062853),
                              (np.nan, np.nan)]})

    location    coor
0   A   (14.48847, 103.161477)
1   B   (14.970084, 103.062853)
2   C   (nan, nan)

```

I tried.

```
df.isna()

    location    coor
0   False   False
1   False   False
2   False   False

df.dropna()

    location    coor
0   A   (14.48847, 103.161477)
1   B   (14.970084, 103.062853)
2   C   (nan, nan)

```

But it isn't work at all. Should i split a tuple into 2 columns or there is a way to deal with thses? Any help or guide would be appreciated.