Add Null/Empty check for param in average method (#4185)

src/main/java/com/thealgorithms/maths/Average.java

@@ -12,6 +12,9 @@ public class Average {
      * @return mean of given numbers
      */
     public static double average(double[] numbers) {
+        if (numbers == null || numbers.length == 0) {
+            throw new IllegalArgumentException("Numbers array cannot be empty or null");
+        }
         double sum = 0;
         for (double number : numbers) {
             sum += number;
@@ -27,6 +30,9 @@ public class Average {
      * @return average value
      */
     public static int average(int[] numbers) {
+        if (numbers == null || numbers.length == 0) {
+            throw new IllegalArgumentException("Numbers array cannot be empty or null");
+        }
         long sum = 0;
         for (int number : numbers) {
             sum += number;