Polish empty check. (spring-projects#3977)

Signed-off-by: Mengqi Xu <[email protected]>

Author: remeio

spring-ai-model/src/main/java/org/springframework/ai/support/UsageCalculator.java

@@ -72,13 +72,7 @@ public static Usage getCumulativeUsage(final Usage currentUsage, final ChatRespo
 	 * @return the boolean value to represent if it is empty.
 	 */
 	public static boolean isEmpty(Usage usage) {
-		if (usage == null) {
-			return true;
-		}
-		else if (usage != null && usage.getTotalTokens() == 0L) {
-			return true;
-		}
-		return false;
+		return usage == null || usage.getTotalTokens() == 0L;
 	}
 
 }