GH-2345: Fix Possible NPE in KafkaAdmin

Resolves #2345

I haven't been able to reproduce it since, but I saw one occasion where
the existing config property returned null.

Protect against an NPE in that case and add the property to the change
candidates.

Also move the map entry out of the for loop.

**cherry-pick to 2.9.x, 2.8.x**

Author: garyrussell

spring-kafka/src/main/java/org/springframework/kafka/core/KafkaAdmin.java

@@ -301,13 +301,12 @@ private Map<ConfigResource, List<ConfigEntry>> checkTopicsForConfigMismatches(
 				if (topicOptional.isPresent() && topicOptional.get().configs() != null) {
 					for (Map.Entry<String, String> desiredConfigParameter : topicOptional.get().configs().entrySet()) {
 						ConfigEntry actualConfigParameter = topicConfig.getValue().get(desiredConfigParameter.getKey());
-						if (!actualConfigParameter.value().equals(desiredConfigParameter.getValue())) {
+						if (!desiredConfigParameter.getValue().equals(actualConfigParameter.value())) {
 							configMismatchesEntries.add(actualConfigParameter);
 						}
-
-						if (configMismatchesEntries.size() > 0) {
-							configMismatches.put(topicConfig.getKey(), configMismatchesEntries);
-						}
+					}
+					if (configMismatchesEntries.size() > 0) {
+						configMismatches.put(topicConfig.getKey(), configMismatchesEntries);
 					}
 				}
 			}

spring-kafka/src/test/java/org/springframework/kafka/core/KafkaAdminTests.java

@@ -152,17 +152,25 @@ public void testAddTopicsAndAddPartitions() throws Exception {
 					&& configResourceConfigMap.get(new ConfigResource(Type.TOPIC, "mismatchconfig")).get("retention.ms").value().equals("11");
 		});
 
-		this.admin.createOrModifyTopics(mismatchconfig);
+		this.admin.createOrModifyTopics(mismatchconfig,
+				TopicBuilder.name("noConfigAddLater")
+						.partitions(2)
+						.replicas(1)
+						.config("retention.ms", "1000")
+						.build());
 
 		await().until(() -> {
 			DescribeConfigsResult describeConfigsResult = this.adminClient
-					.describeConfigs(List.of(new ConfigResource(Type.TOPIC, "mismatchconfig")));
+					.describeConfigs(List.of(new ConfigResource(Type.TOPIC, "mismatchconfig"),
+							new ConfigResource(Type.TOPIC, "noConfigAddLater")));
 			Map<ConfigResource, org.apache.kafka.clients.admin.Config> configResourceConfigMap = describeConfigsResult.all()
 					.get();
 			return configResourceConfigMap.get(new ConfigResource(Type.TOPIC, "mismatchconfig"))
 					.get("retention.bytes").value().equals("1024")
 					&& configResourceConfigMap.get(new ConfigResource(Type.TOPIC, "mismatchconfig"))
-					.get("retention.ms").value().equals("1111");
+					.get("retention.ms").value().equals("1111")
+					&& configResourceConfigMap.get(new ConfigResource(Type.TOPIC, "noConfigAddLater"))
+					.get("retention.ms").value().equals("1000");
 		});
 	}
 
@@ -309,6 +317,14 @@ public NewTopic mismatchconfig() {
 					.build();
 		}
 
+		@Bean
+		public NewTopic noConfigAddLater() {
+			return TopicBuilder.name("noConfigAddLater")
+					.partitions(2)
+					.replicas(1)
+					.build();
+		}
+
 		@Bean
 		public NewTopics topics456() {
 			return new NewTopics(