Improve commit message (#934)

### Motivation
When unspecified a branch name on mirroring setup, the message show with `#null`, we should omit #null when using the default branch to avoid confuse.

Result
Close: #933

it/mirror/src/test/java/com/linecorp/centraldogma/it/mirror/git/GitMirrorTest.java

@@ -233,13 +233,13 @@ void remoteToLocal() throws Exception {
 
  @Test
  void remoteToLocal_gitignore() throws Exception {
- pushMirrorSettings(null, "/first", "\"/exclude_if_root.txt\\nexclude_dir\"");
+ pushMirrorSettings(null, "/first#master", "\"/exclude_if_root.txt\\nexclude_dir\"");
  checkGitignore();
  }
 
  @Test
  void remoteToLocal_gitignore_with_array() throws Exception {
- pushMirrorSettings(null, "/first", "[\"/exclude_if_root.txt\", \"exclude_dir\"]");
+ pushMirrorSettings(null, "/first#master", "[\"/exclude_if_root.txt\", \"exclude_dir\"]");
  checkGitignore();
  }
 

server-mirror-git/src/main/java/com/linecorp/centraldogma/server/internal/mirror/AbstractGitMirror.java

@@ -257,8 +257,9 @@ void mirrorRemoteToLocal(
  changes.put(mirrorStatePath, Change.ofJsonUpsert(
  mirrorStatePath, "{ \"sourceRevision\": \"" + headCommitId.name() + "\" }"));
  // Construct the log message and log.
- summary = "Mirror " + abbrId + ", " + remoteRepoUri() + '#' + remoteBranch() +
- " to the repository '" + localRepo().name() + '\'';
+ final String branchName = getRemoteBranchName(headBranchRef);
+ summary = "Mirror " + abbrId + ", '" + remoteRepoUri() + '#' + branchName +
+ "' to the repository '" + localRepo().name() + '\'';
  final RevCommit headCommit = revWalk.parseCommit(headCommitId);
  detail = generateCommitDetail(headCommit);
  logger.info(summary);
@@ -723,6 +724,18 @@ static void updateRef(org.eclipse.jgit.lib.Repository jGitRepository, RevWalk re
  }
  }
 
+ private String getRemoteBranchName(Ref headBranchRef) {
+ final String remoteBranch = remoteBranch();
+ if (remoteBranch != null && !remoteBranch.isEmpty()) {
+ return remoteBranch;
+ }
+ final String headBranchName = headBranchRef.getName();
+ if (headBranchName.startsWith(Constants.R_HEADS)) {
+ return headBranchName.substring(Constants.R_HEADS.length());
+ }
+ return headBranchName;
+ }
+
  private static final class InsertText extends PathEdit {
  private final ObjectInserter inserter;
  private final String text;