java.lang.NullPointerException in code, can't solve? attempting to find max value

Question

I'm trying to output the max value from a double array using a code sample and I cannot find why the values are being thrown as null, im sorry this is obvious but to my eyes the values have info, or I am misunderstanding something.

I have tried to insert;

 int maximum = t[0];   // start with the first value
for (int i=1; i<t.length; i++) {
    if (t[i] > maximum) {
        maximum = t[i];   // new maximum
    }
}

This is my code:

package test;



import java.util.Scanner;

public class projectone {

public static void main(String[] args) {



// Prepares keyboard as input device 
    Scanner keyboard = new Scanner (System.in);

// Declare variables for user information
    String[] title = new String[20];
    String[] author = new String[20];
    String[] publisher = new String[20];
    Double[] price = new Double[20]; 
    int[] pages = new int[20];
    String[] isbn = new String[20];     

// Declare variables for system information
    int index;
    index = 0;
    int totalbooks;
    totalbooks = 0;
    String temp;

    double sum = 0;
    double total= 0;        

// Loop to prompt user to enter information
    for (index = 0; index < 20; index++)
    {
            System.out.println("Please enter book details,");
            System.out.println("when complete please enter 'nomore' as 'Title'");
            System.out.println("Title :");
            title[index] = keyboard.nextLine();
            if (title[index].contentEquals("nomore"))
            {
                break; //this ends the loop if the user enters 'nomore' in the title field, should
                        // this work in every field?
            }
            System.out.print("Author :");
            author[index] = keyboard.nextLine();                
            System.out.print("Publisher :");
            publisher[index] = keyboard.nextLine(); 

        // The price field is converted from a string to a double, then added to the total count of all
        // previous books prices
            System.out.println("Price :");
            temp = keyboard.nextLine();
            total = Double.valueOf(temp);
            price[index] = Double.valueOf(temp);

            sum = sum += total;

            System.out.print("Page Count :");
            temp = keyboard.nextLine();
            pages[index] = Integer.valueOf(temp);

            System.out.print("ISBN :");
            isbn[index] = keyboard.nextLine();
            totalbooks++; // adds +1 to the total number of books after a new entry

    } // ends data entry loop



    // Prints formatted column names and underlining
            System.out.println(String.format("%-20s", "Title")+
                    String.format("%-20s", "Author")+
                    String.format("%-20s", "Publisher")+
                    String.format("%-20s", "Price")+
                    String.format("%-20s", "Pages")+
                    String.format("%-20s", "ISBN"));
            System.out.println(String.format("%-20s", "====")+
                    String.format("%-20s", "=====")+
                    String.format("%-20s", "=========")+
                    String.format("%-20s", "=======")+
                    String.format("%-20s","=====")+
                    String.format("%-20s","====="));

    // Loop to display entered information 
            for (index = 0; index <totalbooks; index++)
            { 
                System.out.print(String.format("%-20s", title[index])+
                        String.format("%-20s", author[index])+
                        String.format("%-20s", publisher[index])+
                        "£" + String.format("%-20s",  price[index])+ 
                        String.format("%-20s", pages[index])+
                        String.format("%-20s", isbn[index]));
                System.out.println();// line break

            }

    // line breaks
            System.out.println();
            System.out.println();
            System.out.println();

    // data for totals and averages

            System.out.println("Totals");
            System.out.println("-------------------------------");
            System.out.print("Total number of books: "); 
            System.out.println(totalbooks);
            System.out.print("Total cost of books: £");
            System.out.println(sum);



            double max = price[];

                        for (int counter = 1; counter < price.length; counter++)
                        {
                         if (price[counter] > max)
                         {
                          max = price[counter];
                         }
                        }








            System.out.println("Maximum cost of a book :" + max);

            System.out.println("Minimum cost of a book :");

            System.out.print("Average cost of a book :");
            System.out.println(sum/totalbooks);


}
}

I am trying to output the max price, but it keeps throwing

java.lang.NullPointerException

on the line if (price[counter] > max)

I cant figure this out but its probably very obvious, can anyone help?

Thank you