Output from dataframe_to_rows changed from 2.5.1 to 2.5.2

Created originally on Bitbucket by kfollesdal (Kristoffer Føllesdal)

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?