Output from dataframe_to_rows changed from 2.5.1 to 2.5.2
*Created originally on Bitbucket by [kfollesdal (Kristoffer Føllesdal)](https://bitbucket.org/%7Bc2f46baf-5fdb-4cf9-8096-9b321c30e07f%7D/)*
Hi,
noticed that the output from the function dataframe_to_rows in openpyxl.utils.dataframe changed from version 2.5.1 to 2.5.2.
```
#!python
from pandas import DataFrame
from openpyxl.utils.dataframe import dataframe_to_rows
d = DataFrame([1,2,3])
print(list(dataframe_to_rows(d, index=True, header=True)))
```
```
#!python
# Output 2.5.1:
[[None, 0], [0, 1], [1, 2], [2, 3]]
# Output 2.5.2:
[[None, 0], FrozenList([None]), [0, 1], FrozenList([None]), [1, 2], FrozenList([None]), [2, 3]]
```
When we write the result to a worksheet the Forzenlist elements make a blank row in between the data.
This is change of output is probably not intended?
issue