--- a/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialCollectChangesPolicy.java	Tue Dec 09 12:20:05 2014 +0100
+++ b/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialCollectChangesPolicy.java	Tue Dec 16 20:11:05 2014 +0100
@@ -56,8 +56,12 @@
 
   @NotNull
   public RepositoryStateData getCurrentState(@NotNull VcsRoot root) throws VcsException {
+    return getCurrentState(myHgVcsRootFactory.createHgRoot(root));
+  }
+
+  @NotNull
+  public RepositoryStateData getCurrentState(@NotNull final HgVcsRoot hgRoot) throws VcsException {
     final OperationContext context = new OperationContext(myVcs, myRepoFactory, createMercurialProgess());
-    final HgVcsRoot hgRoot = myHgVcsRootFactory.createHgRoot(root);
     VcsCallable<Map<String, String>> cmd = new VcsCallable<Map<String, String>>() {
       public Map<String, String> call() throws VcsException {
         return getHeads(hgRoot, context);
@@ -67,7 +71,7 @@
     String defaultBranchName = hgRoot.getBranchName();
     if (revisions.get(defaultBranchName) == null && !hgRoot.isIgnoreMissingDefaultBranch()) {
       throw new VcsException("Cannot find revision of the default branch '" +
-              defaultBranchName + "' of vcs root " + myVcs.describeVcsRoot(root));
+              defaultBranchName + "' of vcs root " + myVcs.describeVcsRoot(hgRoot));
     }
     return RepositoryStateData.createVersionState(defaultBranchName, revisions);
   }

--- a/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialCommitSupport.java	Tue Dec 09 12:20:05 2014 +0100
+++ b/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialCommitSupport.java	Tue Dec 16 20:11:05 2014 +0100
@@ -25,7 +25,9 @@
 import org.jetbrains.annotations.NotNull;
 
 import java.io.*;
+import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Map;
 import java.util.Set;
 
 public class MercurialCommitSupport implements CommitSupport, MercurialServerExtension {
@@ -130,9 +132,11 @@
     @NotNull
     public CommitResult commit(@NotNull CommitSettings commitSettings) throws VcsException {
       try {
-        RepositoryStateData state = myVcs.getCollectChangesPolicy().getCurrentState(myRoot);
+        RepositoryStateData state = getCurrentState();
         String defaultBranch = state.getDefaultBranchName();
         String defaultBranchRevision = state.getBranchRevisions().get(defaultBranch);
+        if (defaultBranchRevision == null)
+          throw new VcsException("The '" + defaultBranch + "' destination branch doesn't exist");
 
         new CheckoutRepository(myMirrorManager, myHgRepoFactory, myConfig.getPullTimeout(), myConfig.useTagsAsBranches(),
                 myHgRoot, myCheckoutDir).setRevision(defaultBranchRevision).checkout();
@@ -164,10 +168,19 @@
 
         return CommitResult.createSuccessResult(repo.getWorkingDirRevision());
       } catch (Exception e) {
+        if (e instanceof VcsException)
+          throw (VcsException) e;
         throw new VcsException(e);
       }
     }
 
+    @NotNull
+    private RepositoryStateData getCurrentState() throws VcsException {
+      Map<String, String> props = new HashMap<String, String>(myHgRoot.getProperties());
+      props.put(Constants.IGNORE_MISSING_DEFAULT_BRANCH, "true");
+      return myVcs.getCollectChangesPolicy().getCurrentState(new HgVcsRoot(props));
+    }
+
     private String nonEmptyMessage(@NotNull CommitSettings commitSettings) {
       String msg = commitSettings.getDescription();
       if (!StringUtil.isEmpty(msg))

--- a/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialVcsSupport.java	Tue Dec 09 12:20:05 2014 +0100
+++ b/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialVcsSupport.java	Tue Dec 16 20:11:05 2014 +0100
@@ -180,6 +180,11 @@
     return "mercurial: " + vcsRoot.getProperty(Constants.REPOSITORY_PROP);
   }
 
+  @NotNull
+  public String describeVcsRoot(@NotNull final HgVcsRoot vcsRoot) {
+    return "mercurial: " + vcsRoot.getProperty(Constants.REPOSITORY_PROP);
+  }
+
   @Override
   @NotNull
   public TestConnectionSupport getTestConnectionSupport() {

--- a/mercurial-tests/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialCommitSupportTest.java	Tue Dec 09 12:20:05 2014 +0100
+++ b/mercurial-tests/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialCommitSupportTest.java	Tue Dec 16 20:11:05 2014 +0100
@@ -100,6 +100,23 @@
   }
 
 
+  @TestFor(issues = "TW-39321")
+  public void should_throw_meaningful_error_if_destination_branch_doesnt_exist(@NotNull HgVersion _) throws Exception {
+    String nonExistingBranch = "nonExisting";
+    VcsRoot root = vcsRoot().withUrl(myRepo).withBranch(nonExistingBranch).build();
+    String description = "msg";
+    String author = "Joe Doe <joe@some.org>";
+    try {
+      CommitPatchBuilder patchBuilder = myCommitSupport.getCommitPatchBuilder(root);
+      patchBuilder.createFile("a/b/c", stream("test"));
+      patchBuilder.commit(new CommitSettingsImpl(author, description));
+      patchBuilder.dispose();
+    } catch (VcsException e) {
+      assertEquals("The '" + nonExistingBranch + "' destination branch doesn't exist", e.getMessage());
+    }
+  }
+
+
   @NotNull
   private InputStream stream(@NotNull String content) {
     return new ByteArrayInputStream(content.getBytes());