MATLAB: Doesn’t MATLAB’s “readtable” honor the ‘TreatAsEmpty’ option for some strings in the Excel sheet

MATLAB

I have an Excel sheet test.xls with the following data:

Col1Col2Col35abc1 xyz21none3
I try to read this file in with the 'readtable' function using the following command:
>> x = readtable('test.xls', 'TreatAsEmpty', {'none'});
However, I see the following:
x =     Col1     Col2     Col3    ____    ______    ____      5     'abc'     1       NaN     'xyz'     2         1     'none'    3
Why does 'readtable' not replace the last entry in the second column?

>> x.Col2(strcmp(x.Col2, 'none')) = {'NaN'}x =     Col1    Col2     Col3    ____    _____    ____      5     'abc'    1       NaN     'xyz'    2         1     'NaN'    3