[gitg/wip/submodules] Handle displaying of untracked submodules

[Jesse van den Kieboom <jessevdk src gnome org>]

commit 349083602c07bf9f75db410523e1bfafc096ad55
Author: Jesse van den Kieboom <jessevdk gmail com>
Date:   Sun Dec 14 12:07:29 2014 +0100

    Handle displaying of untracked submodules

 gitg/commit/gitg-commit.vala |   43 +++++++++++++++++++++++++++++------------
 1 files changed, 30 insertions(+), 13 deletions(-)
---
diff --git a/gitg/commit/gitg-commit.vala b/gitg/commit/gitg-commit.vala
index 5886794..f612e6d 100644
--- a/gitg/commit/gitg-commit.vala
+++ b/gitg/commit/gitg-commit.vala
@@ -371,20 +371,25 @@ namespace GitgCommit
                        var commit_tree = commit.get_tree();
 
                        var head = d_current_submodule.get_head_id();
-                       Ggit.Commit head_commit;
+                       Ggit.Tree? head_tree = null;
 
-                       try
-                       {
-                               head_commit = repo.lookup<Gitg.Commit>(head);
-                       }
-                       catch (Error e)
+                       if (head != null)
                        {
-                               // TODO: show error to user
-                               stderr.printf("Failed to get head commit: %s\n", e.message);
-                               return;
-                       }
+                               Ggit.Commit head_commit;
+
+                               try
+                               {
+                                       head_commit = repo.lookup<Gitg.Commit>(head);
+                               }
+                               catch (Error e)
+                               {
+                                       // TODO: show error to user
+                                       stderr.printf("Failed to get head commit: %s\n", e.message);
+                                       return;
+                               }
 
-                       var head_tree = head_commit.get_tree();
+                               head_tree = head_commit.get_tree();
+                       }
 
                        Ggit.Diff diff;
 
@@ -443,12 +448,24 @@ namespace GitgCommit
                        if (type == IndexType.STAGED)
                        {
                                model.set_include(new Ggit.OId[] { submodule.get_index_id() });
-                               model.set_exclude(new Ggit.OId[] { submodule.get_head_id() });
+
+                               var head_id = submodule.get_head_id();
+
+                               if (head_id != null)
+                               {
+                                       model.set_exclude(new Ggit.OId[] { head_id });
+                               }
                        }
                        else
                        {
+                               var index_id = submodule.get_index_id();
+
                                model.set_include(new Ggit.OId[] { submodule.get_workdir_id() });
-                               model.set_exclude(new Ggit.OId[] { submodule.get_index_id() });
+
+                               if (index_id != null)
+                               {
+                                       model.set_exclude(new Ggit.OId[] { index_id });
+                               }
                        }
 
                        d_submodule_history_select_first = true;