Miscellaneous cleanup in the supervisor API flow. (apache#17144)

Extracting a few miscellaneous non-functional changes from the batch supervisor branch:

- Replace anonymous inner classes with lambda expressions in the SQL supervisor manager layer
- Add explicit @nullable annotations in DynamicConfigProviderUtils to make IDE happy
- Small variable renames (copy-paste error perhaps) and fix typos
- Add table name for this exception message: Delete the supervisor from the table[%s] in the database...
- Prefer CollectionUtils.isEmptyOrNull() over list == null || list.size() > 0. We can change the Precondition checks to throwing DruidException separately for a batch of APIs at a time.

indexing-service/src/main/java/org/apache/druid/indexing/overlord/supervisor/SupervisorResource.java

@@ -50,6 +50,7 @@
 import org.apache.druid.server.security.Resource;
 import org.apache.druid.server.security.ResourceAction;
 import org.apache.druid.server.security.ResourceType;
+import org.apache.druid.utils.CollectionUtils;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -123,7 +124,7 @@ public Response specPost(final SupervisorSpec spec, @Context final HttpServletRe
     return asLeaderWithSupervisorManager(
         manager -> {
           Preconditions.checkArgument(
-              spec.getDataSources() != null && spec.getDataSources().size() > 0,
+              !CollectionUtils.isNullOrEmpty(spec.getDataSources()),
               "No dataSources found to perform authorization checks"
           );
           final Set<ResourceAction> resourceActions;
@@ -412,7 +413,7 @@ public Response shutdown(@PathParam("id") final String id)
   public Response handoffTaskGroups(@PathParam("id") final String id, @Nonnull final HandoffTaskGroupsRequest handoffTaskGroupsRequest)
   {
     List<Integer> taskGroupIds = handoffTaskGroupsRequest.getTaskGroupIds();
-    if (taskGroupIds == null || taskGroupIds.isEmpty()) {
+    if (CollectionUtils.isNullOrEmpty(taskGroupIds)) {
       return Response.status(Response.Status.BAD_REQUEST)
           .entity(ImmutableMap.of("error", "List of task groups to handoff can't be empty"))
           .build();
@@ -533,7 +534,7 @@ public Response specGetHistory(
                         authorizerMapper
                     )
                 );
-            if (authorizedHistoryForId.size() > 0) {
+            if (!authorizedHistoryForId.isEmpty()) {
               return Response.ok(authorizedHistoryForId).build();
             }
           }

processing/src/main/java/org/apache/druid/utils/DynamicConfigProviderUtils.java

@@ -22,13 +22,14 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import org.apache.druid.metadata.DynamicConfigProvider;
 
+import javax.annotation.Nullable;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
 public class DynamicConfigProviderUtils
 {
-  public static Map<String, String> extraConfigAndSetStringMap(Map<String, Object> config, String dynamicConfigProviderKey, ObjectMapper mapper)
+  public static Map<String, String> extraConfigAndSetStringMap(@Nullable Map<String, Object> config, String dynamicConfigProviderKey, ObjectMapper mapper)
   {
     HashMap<String, String> newConfig = new HashMap<>();
     if (config != null) {
@@ -43,7 +44,7 @@ public static Map<String, String> extraConfigAndSetStringMap(Map<String, Object>
     return newConfig;
   }
 
-  public static Map<String, Object> extraConfigAndSetObjectMap(Map<String, Object> config, String dynamicConfigProviderKey, ObjectMapper mapper)
+  public static Map<String, Object> extraConfigAndSetObjectMap(@Nullable Map<String, Object> config, String dynamicConfigProviderKey, ObjectMapper mapper)
   {
     HashMap<String, Object> newConfig = new HashMap<>();
     if (config != null) {
@@ -58,7 +59,7 @@ public static Map<String, Object> extraConfigAndSetObjectMap(Map<String, Object>
     return newConfig;
   }
 
-  private static Map<String, String> extraConfigFromProvider(Object dynamicConfigProviderJson, ObjectMapper mapper)
+  private static Map<String, String> extraConfigFromProvider(@Nullable Object dynamicConfigProviderJson, ObjectMapper mapper)
   {
     if (dynamicConfigProviderJson != null) {
       DynamicConfigProvider dynamicConfigProvider = mapper.convertValue(dynamicConfigProviderJson, DynamicConfigProvider.class);