fix(math): handle null and empty inputs in average methods (#760)

Author: SYaoJun

geaflow/geaflow-utils/src/main/java/org/apache/geaflow/utils/math/MathUtil.java

@@ -184,6 +184,9 @@ private static long[] toArray(List<Long> input) {
      * @return The average(values)
      */
     public static long average(long[] values) {
+        if (values == null || values.length == 0) {
+            return 0;
+        }
         //Find average
         double sum = 0d;
         for (long value : values) {
@@ -198,6 +201,9 @@ public static long average(long[] values) {
      * @return The average(values)
      */
     public static long average(List<Long> values) {
+        if (values == null || values.isEmpty()) {
+            return 0;
+        }
         //Find average
         double sum = 0d;
         for (long value : values) {

geaflow/geaflow-utils/src/test/java/org/apache/geaflow/utils/math/MathUtilTest.java

@@ -19,6 +19,7 @@
 
 package org.apache.geaflow.utils.math;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import org.testng.Assert;
@@ -69,6 +70,32 @@ public void testAverage() {
         Assert.assertEquals(7, result);
     }
 
+    @Test
+    public void testAverageEmptyArray() {
+        // Test empty array returns 0
+        long[] emptyArray = new long[0];
+        long result = MathUtil.average(emptyArray);
+        Assert.assertEquals(0, result);
+
+        // Test null array returns 0
+        long[] nullArray = null;
+        result = MathUtil.average(nullArray);
+        Assert.assertEquals(0, result);
+    }
+
+    @Test
+    public void testAverageEmptyList() {
+        // Test empty list returns 0
+        List<Long> emptyList = new ArrayList<>();
+        long result = MathUtil.average(emptyList);
+        Assert.assertEquals(0, result);
+
+        // Test null list returns 0
+        List<Long> nullList = null;
+        result = MathUtil.average(nullList);
+        Assert.assertEquals(0, result);
+    }
+
     @Test
     public void testMedian() {
         List<Long> array = Arrays.asList(1L, 2L, 8L, 9L, 13L, 3L, 12L, 4L, 7L, 6L, 11L, 10L, 5L);