Accept empty config values in the Lettuce connection wrapper.

Closes #2798

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

@@ -220,7 +220,7 @@ class LettuceClusterServerCommands extends LettuceServerCommands implements Redi
 	public void setConfig(String param, String value) {
 
 		Assert.hasText(param, "Parameter must not be null or empty");
-		Assert.hasText(value, "Value must not be null or empty");
+		Assert.notNull(value, "Value must not be null");
 
 		executeCommandOnAllNodes(client -> client.configSet(param, value));
 	}

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

@@ -130,7 +130,7 @@ class LettuceReactiveServerCommands implements ReactiveServerCommands {
 	public Mono<String> setConfig(String param, String value) {
 
 		Assert.hasText(param, "Parameter must not be null or empty");
-		Assert.hasText(value, "Value must not be null or empty");
+		Assert.notNull(value, "Value must not be null");
 
 		return connection.execute(c -> c.configSet(param, value)).next();
 	}

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

@@ -145,7 +145,7 @@ class LettuceServerCommands implements RedisServerCommands {
 	public void setConfig(String param, String value) {
 
 		Assert.hasText(param, "Parameter must not be null or empty");
-		Assert.hasText(value, "Value must not be null or empty");
+		Assert.notNull(value, "Value must not be null");
 
 		connection.invokeStatus().just(RedisServerAsyncCommands::configSet, param, value);
 	}

src/test/java/org/springframework/data/redis/connection/lettuce/LettuceReactiveServerCommandsIntegrationTests.java

@@ -215,6 +215,23 @@ public class LettuceReactiveServerCommandsIntegrationTests extends LettuceReacti
 		}
 	}
 
+	@ParameterizedRedisTest // GH-2798
+	void setConfigShouldRespondCorrectly() {
+
+		if (!(connection instanceof LettuceReactiveRedisClusterConnection)) {
+
+			connection.serverCommands().setConfig("notify-keyspace-events", "") //
+					.as(StepVerifier::create) //
+					.expectNext("OK")
+					.verifyComplete();
+
+			connection.serverCommands().setConfig("notify-keyspace-events", "KEA") //
+					.as(StepVerifier::create) //
+					.expectNext("OK")
+					.verifyComplete();
+		}
+	}
+
 	@ParameterizedRedisTest // DATAREDIS-659
 	void setConfigShouldApplyConfiguration() {
 

src/test/java/org/springframework/data/redis/core/RedisKeyValueAdapterTests.java

@@ -91,6 +91,7 @@ public class RedisKeyValueAdapterTests {
 		RedisConnection connection = template.getConnectionFactory().getConnection();
 
 		try {
+			connection.setConfig("notify-keyspace-events", "");
 			connection.setConfig("notify-keyspace-events", "KEA");
 		} finally {
 			connection.close();