arrays are giving me null reference exceptions and I don't know why

Hi, I'm my arrays are giving me alot of problems. I create an array and set it's size then I try to assign float's to it but I get a "NullReferenceException: Object reference not set to an instance of an object" error. here is the some of my code. Unity says the error is where secondArr is being assigned a variable for a the i'th position.

 var firstArr:String[] = new String[length];
 var secondArr:float[] = new float[length];
 
 for(var i= 0; i < newDataParsed["data"].length; i++){
 
 if(newDataParsed["data"][i][key] == key2){
 
 firstArr[i] = newDataParsed["data"][i][key3];
 secondArr[i] = newDataParsed["data"][i][key4];
 }