refactor(engine): Code Review points

- Remove execute method from FetchAndLockBuilder
- Refactor FetchAndLockBuilderImpl to use a List instead of a Map and make it similar to the QueryAPI for the sake of consistency
- Add tests for covering invalid usages of fetchAndLock API
- Infer useCreateTime
- Correct JavaDoc
- Generify Sorting of FetchAndLock Impl
- Remove var

engine-rest/engine-rest/src/main/java/org/camunda/bpm/engine/rest/dto/externaltask/FetchExternalTasksDto.java

@@ -203,19 +203,19 @@ public void setIncludeExtensionProperties(boolean includeExtensionProperties) {
     }
   }
 
-  public FetchAndLockBuilder buildQuery(ProcessEngine processEngine) {
+  public ExternalTaskQueryTopicBuilder buildQuery(ProcessEngine processEngine) {
     FetchAndLockBuilder fetchAndLockBuilder = getBuilder(processEngine);
 
-    if (CollectionUtil.isEmpty(topics)) {
-      return fetchAndLockBuilder;
-    }
-
     return configureTopics(fetchAndLockBuilder);
   }
 
-  protected FetchAndLockBuilder configureTopics(FetchAndLockBuilder builder) {
+  protected ExternalTaskQueryTopicBuilder configureTopics(FetchAndLockBuilder builder) {
     ExternalTaskQueryTopicBuilder topicBuilder = builder.subscribe();
 
+    if (CollectionUtil.isEmpty(topics)) {
+      return topicBuilder;
+    }
+
     topics.forEach(topic -> {
       topicBuilder.topic(topic.getTopicName(), topic.getLockDuration());
 
@@ -272,7 +272,7 @@ protected FetchAndLockBuilder configureTopics(FetchAndLockBuilder builder) {
       }
     });
 
-    return builder;
+    return topicBuilder;
   }
 
   protected FetchAndLockBuilder getBuilder(ProcessEngine engine) {

engine-rest/engine-rest/src/main/java/org/camunda/bpm/engine/rest/impl/FetchAndLockHandlerImpl.java

@@ -29,7 +29,7 @@
 import javax.ws.rs.core.Response.Status;
 import org.camunda.bpm.engine.IdentityService;
 import org.camunda.bpm.engine.ProcessEngine;
-import org.camunda.bpm.engine.externaltask.FetchAndLockBuilder;
+import org.camunda.bpm.engine.externaltask.ExternalTaskQueryTopicBuilder;
 import org.camunda.bpm.engine.externaltask.LockedExternalTask;
 import org.camunda.bpm.engine.impl.ProcessEngineImpl;
 import org.camunda.bpm.engine.impl.identity.Authentication;
@@ -262,8 +262,9 @@ protected FetchAndLockResult tryFetchAndLock(FetchAndLockRequest request) {
   }
 
   protected List<LockedExternalTaskDto> executeFetchAndLock(FetchExternalTasksExtendedDto fetchingDto, ProcessEngine processEngine) {
-    FetchAndLockBuilder fetchBuilder = fetchingDto.buildQuery(processEngine);
+    ExternalTaskQueryTopicBuilder fetchBuilder = fetchingDto.buildQuery(processEngine);
     List<LockedExternalTask> externalTasks = fetchBuilder.execute();
+
     return LockedExternalTaskDto.fromLockedExternalTasks(externalTasks);
   }