Looping through a specific bit of text gives me unstable result

Hi! 

Working with text wanting to be able to specify which exact part of the whole text I want to fetch. The setup now is Point Expression Control that defines the start and the end of the splitted string and render it using a for loop. It works, but. The result is unstable when I'm changing the start value, often it gets stuck at "UNDEFINIED". 

t = thisComp.layer("txtSource").text.sourceText; 
t = t.split(" ");
txtFrom = effect("txt FromTo ")("Point")[0]; 
txtTo = effect("txt FromTo ")("Point")[1]; 
t2 = "";
for (i = txtFrom; i < txtTo; i++) {
	t2 += t[i] + " ";
}

l1 = thisComp.layer("Font STYLE 1").text.sourceText;
l2 = thisComp.layer("Font STYLE 2").text.sourceText;
l3 = thisComp.layer("Font STYLE 3").text.sourceText;


textStyles = [l1, l2, l3];
c = clamp(effect("current style")("Slider"), 0, textStyles.length-1);


style = textStyles[c].getStyleAt(0,0);
style.setText(t2);

that's the entire code, that also fetches styles from three different layers. 

I'm guessing there is some kind of try or break function that I need to add? Anyone has an idea how to make this more stable?