I have a dataframe (`df`) which looks like:

```
Date        Last Value
29/12/2017      45.675
28/12/2017           0
27/12/2017      45.665
26/12/2017      45.635
25/12/2017  
22/12/2017      45.625
21/12/2017      45.645
20/12/2017      45.655
19/12/2017      45.689

```

How can I return rows that have either a blank or a zero only? So the desired returned output from the above would be:

```
28/12/2017           0
25/12/2017  

```

Where the values are either blank or 0.