How can i trace a matlab modelling code, generated through GUI for decision tree classifer?

i am kind of trying to get an understanding over the decision tree algorithm of matlab. To get some clarification over the cross validation. i have a built a model using my data. And started to trace the code line by line. where i got a fatal. have provided the few lines of modelling code generated by matlab for your reference.

    function [trainedClassifier, validationAccuracy] = trainClassifier(trainingData)
    predictorNames = {'FIT101', 'LIT101', 'MV101', 'P101'};
    predictors = inputTable(:, predictorNames);

I got the error in the predictors = inputTable(:, predictorNames); it shows error like the kind of function is not defined for cellarray, the variable predictorNames is a cell array. i dont know what other errors would occur if i clear this error and run further line by line.

But this code is what built by matlab and shows some results too, the how can it fail when i run it line by line?

How can i trace this modelling code by myself by having the data in the workspace?

Any help would be greatly appreciated.

Thanks,