Why do I receive "Error using sort:Input argument must be a cell array of character vectors"

When I transform CSV to MAT,below error appears.The reason is that the data in the CSV file is not always existing, right?

Error in matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)DataAnalysisTool('Convert_Callback',hObject,eventdata,guidata(hObject))

Error while evaluating UIControl Callback.

Error using sort

Input argument must be a cell array of character vectors.

[Walter Roberson]

We need to see the code for Convert_Callback