Fix ZAddArgs.isEmpty.

isEmpty now returns true if empty. Previously, the boolean returns were flipped.

Closes #2588

Author: mp911de

src/main/java/org/springframework/data/redis/connection/RedisZSetCommands.java

@@ -504,7 +504,7 @@ public boolean contains(Flag flag) {
 		 * @return {@literal true} if no flags set.
 		 */
 		public boolean isEmpty() {
-			return !flags.isEmpty();
+			return flags.isEmpty();
 		}
 
 		@Override

src/main/java/org/springframework/data/redis/connection/jedis/JedisConverters.java

@@ -689,7 +689,7 @@ public static GeoUnit toGeoUnit(Metric metric) {
 	 */
 	static ZAddParams toZAddParams(ZAddArgs source) {
 
-		if (!source.isEmpty()) {
+		if (source.isEmpty()) {
 			return new ZAddParams();
 		}
 

src/main/java/org/springframework/data/redis/connection/lettuce/LettuceZSetCommands.java

@@ -894,7 +894,7 @@ private static io.lettuce.core.ZAddArgs toZAddArgs(ZAddArgs source) {
 
 		io.lettuce.core.ZAddArgs target = new io.lettuce.core.ZAddArgs();
 
-		if (!source.isEmpty()) {
+		if (source.isEmpty()) {
 			return target;
 		}
 

src/test/java/org/springframework/data/redis/connection/RedisZSetCommandsUnitTests.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.redis.connection;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.data.redis.connection.RedisZSetCommands.ZAddArgs;
+
+/**
+ * Unit tests for {@link RedisZSetCommands}.
+ *
+ * @author Mark Paluch
+ */
+class RedisZSetCommandsUnitTests {
+
+	@Test // GH-2588
+	void zAddArgsShouldReportEmpty() {
+
+		assertThat(ZAddArgs.empty().isEmpty()).isTrue();
+		assertThat(ZAddArgs.ifExists().isEmpty()).isFalse();
+	}
+}