Python problem reading CSV files that contain the word NUL

Question

I have a short Python script for reading CSV files. So far nothing special.

def csvReader(filename):

    return csv.reader(open(filename,'tr', encoding='utf-8'))
  
for row in csvReader('test.csv'):
    print(row)

However, it triggers an error message if the CSV file contains the word "NUL" in a field. E.g. like this:

timestamp_utc,id, text,key

2021-07-15 13:47:01,12345,"Some text,sfghj",z3O9ZNULdxBfR

If I now read in this CSV file (which, by the way, is not created by me, it is delivered externally), I get this error message:

_csv.Error: line contains NUL

Curiously, if I open the file in the simple Windows editor and save it without changing anything, the error does not occur and the file is processed normally.

General conditions: Windows, Pycharm, Python 3.8