[Spotbugs] Enable spotbugs in pulsar-metadata (apache#9253)

Fixes streamnative/pulsar#1797

### Motivation

Enable spotbugs in module pulsar-metadata.

pulsar-metadata/pom.xml

@@ -54,4 +54,26 @@
       <artifactId>caffeine</artifactId>
     </dependency>
   </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>com.github.spotbugs</groupId>
+        <artifactId>spotbugs-maven-plugin</artifactId>
+        <version>${spotbugs-maven-plugin.version}</version>
+        <configuration>
+          <excludeFilterFile>${basedir}/src/test/resources/findbugsExclude.xml</excludeFilterFile>
+        </configuration>
+        <executions>
+          <execution>
+            <id>spotbugs</id>
+            <phase>verify</phase>
+            <goals>
+              <goal>check</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>

pulsar-metadata/src/main/java/org/apache/pulsar/metadata/api/GetResult.java

@@ -25,7 +25,6 @@
  */
 @Data
 public class GetResult {
-
     /**
      * The value of the key stored.
      */

pulsar-metadata/src/main/java/org/apache/pulsar/metadata/coordination/impl/LeaderElectionImpl.java

@@ -108,8 +108,8 @@ private synchronized CompletableFuture<LeaderElectionState> elect() {
                             log.warn("Exception in state change listener", t);
                         }
                     }
+                    return CompletableFuture.completedFuture(leaderElectionState);
                 }
-                return CompletableFuture.completedFuture(leaderElectionState);
             } else {
                 return tryToBecomeLeader();
             }
@@ -143,8 +143,8 @@ private synchronized CompletableFuture<LeaderElectionState> tryToBecomeLeader()
                                                     log.warn("Exception in state change listener", t);
                                                 }
                                             }
+                                            result.complete(leaderElectionState);
                                         }
-                                        result.complete(leaderElectionState);
                                     }).exceptionally(ex -> {
                                         // We fail to do the get(), so clean up the leader election fail the whole
                                         // operation

pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/LocalMemoryMetadataStore.java

@@ -173,7 +173,7 @@ public synchronized CompletableFuture<Void> storeDelete(String path, Optional<Lo
         Value value = map.get(path);
         if (value == null) {
             return FutureUtils.exception(new NotFoundException(""));
-        } else if (value != null && optExpectedVersion.isPresent() && optExpectedVersion.get() != value.version) {
+        } else if (optExpectedVersion.isPresent() && optExpectedVersion.get() != value.version) {
             return FutureUtils.exception(new BadVersionException(""));
         } else {
             map.remove(path);
@@ -191,6 +191,6 @@ private static boolean isValidPath(String path) {
             return false;
         }
 
-        return path != "/" || !path.endsWith("/");
+        return !path.equals("/") || !path.endsWith("/");
     }
 }

pulsar-metadata/src/test/resources/findbugsExclude.xml

@@ -0,0 +1,26 @@
+<!--
+
+    Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
+    distributed with this work for additional information
+    regarding copyright ownership.  The ASF licenses this file
+    to you 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
+
+      http://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.
+
+-->
+<FindBugsFilter>
+    <Match>
+        <Class name="org.apache.pulsar.metadata.api.GetResult" />
+        <Bug pattern="EI_EXPOSE_REP,EI_EXPOSE_REP2" />
+    </Match>
+</FindBugsFilter>