How to create a linked list array in Java?

So I need to input the edges of a bipartite graph like this:

6
1 3
1 2
1 5
2 7
2 4
2 9

The first number is the number of sides Then list the edges Seeing how vertex 1 has multiple different edges, I want to track what 1 is connected to. I'm thinking that each vertex of the graph will have some lists. The vertices it connects lead me to try to create a linked list array, but I don't know what to do I tried

LinkedList<Integer>[] vertex = new LinkedList[5];
int i = 0,m = 6;
while(i!=m){
    int temp = sc.nextInt();
    int temp2 = sc.nextInt();
    vertex[temp].add(temp2);
    i++;
}

But I get a NullPointerException on the addition line

Solution

LinkedList<Integer>[] vertex = new LinkedList[5];

LinkedList<Integer>[] vertex = new LinkedList[5];
int i = 0,m = 6;
while(i!=m){
  int temp = sc.nextInt();
  int temp2 = sc.nextInt();

  // Make sure the list is initialized before adding to it
  if (vertex[temp] == null) {
     vertex[temp] = new LinkedList<Integer>();
  }

  vertex[temp].add(temp2);
  i++;
}