Fix more cases where Collection.isEmpty() should be used

Change-Id: I9c8465445373179f928f33e57dae83c9027b7a9f

java/com/google/gerrit/pgm/init/api/Section.java

@@ -69,7 +69,7 @@ public class Section {
     all.addAll(Arrays.asList(flags.cfg.getStringList(section, subsection, name)));
 
     if (value != null) {
-      if (all.size() == 0 || all.size() == 1) {
+      if (all.isEmpty() || all.size() == 1) {
         flags.cfg.setString(section, subsection, name, value);
       } else {
         all.set(0, value);
@@ -78,7 +78,7 @@ public class Section {
 
     } else if (all.size() == 1) {
       flags.cfg.unset(section, subsection, name);
-    } else if (all.size() != 0) {
+    } else if (!all.isEmpty()) {
       all.remove(0);
       flags.cfg.setStringList(section, subsection, name, all);
     }

java/com/google/gerrit/server/git/GroupCollector.java

@@ -167,7 +167,7 @@ public class GroupCollector {
     checkState(!done, "visit() called after getGroups()");
     Set<RevCommit> interestingParents = getInterestingParents(c);
 
-    if (interestingParents.size() == 0) {
+    if (interestingParents.isEmpty()) {
       // All parents are uninteresting: treat this commit as the root of a new
       // group of related changes.
       groups.put(c, c.name());

java/com/google/gerrit/server/git/receive/ReceiveCommits.java

@@ -2159,7 +2159,7 @@ class ReceiveCommits {
           return Collections.emptyList();
         }
 
-        if (changes.size() == 0) {
+        if (changes.isEmpty()) {
           if (!isValidChangeId(p.changeKey.get())) {
             reject(magicBranch.cmd, "invalid Change-Id");
             return Collections.emptyList();

java/com/google/gerrit/server/restapi/account/DeleteExternalIds.java

@@ -72,7 +72,7 @@ public class DeleteExternalIds implements RestModifyView<AccountResource, List<S
       permissionBackend.currentUser().check(GlobalPermission.ACCESS_DATABASE);
     }
 
-    if (extIds == null || extIds.size() == 0) {
+    if (extIds == null || extIds.isEmpty()) {
       throw new BadRequestException("external IDs are required");
     }
 

java/com/google/gerrit/server/restapi/change/ReviewerRecommender.java

@@ -238,7 +238,7 @@ public class ReviewerRecommender {
     // (weighted 10d), number of comments (weighted 0.5d) and number of owned
     // changes (weighted 1d).
     Map<Account.Id, MutableDouble> reviewers = new LinkedHashMap<>();
-    if (candidates.size() == 0) {
+    if (candidates.isEmpty()) {
       return reviewers;
     }
     List<Predicate<ChangeData>> predicates = new ArrayList<>();