style: fix formatting in StringUtils and StringUtilsTest, update toCommaDelimitedString to return null when inputs are null, adjust tests for correct null handling, and ensure spotless compliance

Author: ankitshokeen

dubbo-common/src/main/java/org/apache/dubbo/common/utils/StringUtils.java

@@ -1242,14 +1242,17 @@ public static byte decodeHexByte(CharSequence s, int pos) {
     }
 
     /**
-     * Create the common-delimited {@link String} by one or more {@link String} members
+     * Creates a comma-delimited string from one or more string values.
      *
-     * @param one    one {@link String}
-     * @param others others {@link String}
-     * @return <code>null</code> if <code>one</code> or <code>others</code> is <code>null</code>
+     * @param one    the first string value
+     * @param others additional string values
+     * @return a combined comma-delimited string, or <code>null</code> if {@code one} or {@code others} is {@code null}
      * @since 2.7.8
      */
     public static String toCommaDelimitedString(String one, String... others) {
+        if (one == null || others == null) {
+            return null;
+        }
         String another = arrayToDelimitedString(others, COMMA_SEPARATOR);
         return isEmpty(another) ? one : one + COMMA_SEPARATOR + another;
     }

dubbo-common/src/test/java/org/apache/dubbo/common/utils/StringUtilsTest.java

@@ -35,7 +35,6 @@
 import static org.apache.dubbo.common.utils.StringUtils.splitToList;
 import static org.apache.dubbo.common.utils.StringUtils.splitToSet;
 import static org.apache.dubbo.common.utils.StringUtils.startsWithIgnoreCase;
-import static org.apache.dubbo.common.utils.StringUtils.toCommaDelimitedString;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
@@ -478,22 +477,22 @@ private void assertEqualsWithoutSpaces(String expect, String actual) {
      */
     @Test
     void testToCommaDelimitedString() {
-        String value = toCommaDelimitedString(null);
+        String value = StringUtils.toCommaDelimitedString(null);
         assertNull(value);
 
-        value = toCommaDelimitedString(null, null);
+        value = StringUtils.toCommaDelimitedString(null, (String) null);
         assertNull(value);
 
-        value = toCommaDelimitedString("");
+        value = StringUtils.toCommaDelimitedString("");
         assertEquals("", value);
 
-        value = toCommaDelimitedString("one");
+        value = StringUtils.toCommaDelimitedString("one");
         assertEquals("one", value);
 
-        value = toCommaDelimitedString("one", "two");
+        value = StringUtils.toCommaDelimitedString("one", "two");
         assertEquals("one,two", value);
 
-        value = toCommaDelimitedString("one", "two", "three");
+        value = StringUtils.toCommaDelimitedString("one", "two", "three");
         assertEquals("one,two,three", value);
     }