key error when collating results from shorter monitoring periods

[smallsr]

A key error consistently occurs when using accUtils.collateJSONfilesToSingleCSV when collating summary files from shorter monitoring periods (e.g. 24 hours or less). Interestingly, a workaround is to place a single summary json from a longer monitoring time into the folder with the shorter summary json files. This extra file must have been processed with the same activity model as the current files of interest. When this extra summary file is in place, the script runs without error.
The key error is below:

accUtils.collateJSONfilesToSingleCSV("full_clemson_results/summary/", "xyz.csv")
Traceback (most recent call last):
File "", line 1, in
File "/mnt/c/Users/srsma/mar2021_biobankAccelerometerAnalysis/biobankAccelerometerAnalysis/accelerometer/accUtils.py", line 241, in collateJSONfilesToSingleCSV
dAcc = df[list(refColumnItem.keys())] #maintain intended column ordering
AttributeError: 'NoneType' object has no attribute 'keys'