Exception in thread main java.lang.NullPointerException

public class MTBFTester
 {
        public static void main (String [] args)
        {
        usage(args);
        MTBFCalculator calc = new MTBFCalculator(args);
        calc.getMTBF();
        }
        private static void usage(String [] test)
        {
        if (test.length<2)
        {
        System.out.println("usage: java MTBFTester <1st value> <2nd 
value> ...");
        }
    }
}

//This is the other class
class MTBFCalculator
{

//fields
        String [] argsArray;
        double [] doublesArray;
//constructor
        public MTBFCalculator(String [] data)
        {
        for(int i=0; i<data.length; i++)
 {
        argsArray  = data ;
        }
        doublesArray = new double[argsArray.length];
        }
//method
        public void getMTBF()
        {
        for(int i=0; i<argsArray.length; i++)
        {
        doublesArray = Double.parseDouble(argsArray);
        if (doublesArray < 1)
        {
        System.out.println("zero or negative values are not accepted");
        }
                }
                double testMTBF = 0;
                double MTBF = 0;
                for(int i=0; i<doublesArray.length; i++)
                {
                testMTBF = testMTBF + 1/doublesArray;
                }
                MTBF = 1/testMTBF;
                System.out.println("" + MTBF);
       }
}