Color applied object change color

I wrote this code

But I am getting the error Why?

var findC = [

"C=100 M=0 Y=0 K=0",

"C=0 M=0 Y=100 K=0"

]

changeC = [

"C=15 M=100 Y=100 K=0",

"C=75 M=5 Y=100 K=0"

]

var doc = app.activeDocument; 

app.findObjectPreferences = app.changeObjectPreferences = null; 

for(var i = 0; i < findC.length; ++i) {

app.findObjectPreferences.fillColor = app.activeDocument.swatches.itemByName(findC);

app.changeObjectPreferences.fillColor =app.activeDocument.swatches.itemByName(changeC);

app.changeObject(); 

      }

app.findObjectPreferences = app.changeObjectPreferences = null;