Update state check error message to include failure hint.

Original Pull Request: #2013

Author: christophstrobl

Diff for: src/main/java/org/springframework/data/redis/connection/lettuce/LettuceConnectionFactory.java

@@ -820,9 +820,7 @@ public AbstractRedisClient getRequiredNativeClient() {
 
 		AbstractRedisClient client = getNativeClient();
 
-		if (client == null) {
-			throw new IllegalStateException("Client not yet initialized");
-		}
+		Assert.state(client != null, "Client not yet initialized. Did you forget to call initialize the bean?");
 
 		return client;
 	}

Diff for: src/test/java/org/springframework/data/redis/connection/lettuce/LettuceConnectionFactoryUnitTests.java

@@ -1011,7 +1011,7 @@ void getNativeClientShouldFailIfNotInitialized() {
 		LettuceConnectionFactory connectionFactory = new LettuceConnectionFactory();
 
 		assertThatIllegalStateException().isThrownBy(connectionFactory::getRequiredNativeClient)
-				.withMessage("Client not yet initialized");
+				.withMessageContaining("Client not yet initialized");
 	}
 
 	@Data