Set the last value of a dynamic array of char pointers in C to NULL for while loop termination?

Question

I have a few questions based off the code below.

1. Would this be the correct way to have a sentinel value of NULL at the end of this dynamic array of char pointers? If not what could I do?
2. Will the code below cause a memory leak because I am setting malloced memory to NULL?

My general question would be.

1. What could I possibly do so that I can have a dynamic array of character pointers with the last value to be NULL so I can stop the loop at that point without keeping a count of how many elements in the dynamic array of character pointers.

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int i = 0;
    char **array_strings = NULL;
    array_strings = malloc(sizeof(char *) * 2);
    array_strings[0] = malloc(sizeof(char) * 5);
    strcpy(array_strings[0],"test");
    array_strings[1]=NULL;
    while (array_strings[i] != NULL)
    {
        printf("array_strings[%d]: %s", i, array_strings[i]);
        i++;
    }
    free(array_strings[0]);
    free(array_strings[1]);
    free(array_strings);
    return 0;
}