recover from bad shas

lib/gollum/git_access.rb

@@ -47,8 +47,9 @@ module Gollum
     end
 
     def tree(ref)
-      sha = ref_to_sha(ref)
-      get_cache(:tree, sha) { tree!(sha) }
+      if sha = ref_to_sha(ref)
+        get_cache(:tree, sha) { tree!(sha) }
+      end
     end
 
     def blob(sha)
@@ -62,9 +63,10 @@ module Gollum
         if sha = get_cache(:ref, ref)
           commit(sha)
         else
-          cm = commit!(ref)
-          set_cache(:ref,    ref,   cm.id)
-          set_cache(:commit, cm.id, cm)
+          if cm = commit!(ref)
+            set_cache(:ref,    ref,   cm.id)
+            set_cache(:commit, cm.id, cm)
+          end
         end
       end
     end
@@ -95,6 +97,7 @@ module Gollum
 
     def ref_to_sha!(ref)
       @repo.git.rev_list({:max_count=>1}, ref)
+    rescue Grit::GitRuby::Repository::NoSuchShaFound
     end
 
     def tree!(sha)
@@ -119,12 +122,12 @@ module Gollum
       if value.nil? && block_given?
         set_cache(name, key, value = yield)
       end
-      value
+      value == :_nil ? nil : value
     end
 
     def set_cache(name, key, value)
       cache      = instance_variable_get("@#{name}_map")
-      cache[key] = value
+      cache[key] = value || :_nil
     end
 
     def multi_get(name, keys)

lib/gollum/page.rb

@@ -289,7 +289,7 @@ module Gollum
     #
     # Returns a Gollum::Page or nil if the page could not be found.
     def find_page_in_tree(map, name, checked_dir = nil)
-      return nil if name.to_s.empty?
+      return nil if !map || name.to_s.empty?
       if checked_dir = BlobEntry.normalize_dir(checked_dir)
         checked_dir.downcase!
       end

test/test_git_access.rb

@@ -15,7 +15,6 @@ context "GitAccess" do
 
   test "#commits uses commit_map" do
     actual = @access.repo.commits.first
-    #@access.commit actual.id
     @access.commit_map['abc'] = 1
     commits = @access.commits('abc', actual.id)
     assert_equal 1, commits[0]
@@ -27,7 +26,7 @@ context "GitAccess" do
     assert @access.tree_map.empty?
     @access.tree 'master'
     assert_equal({"master"=>"60f12f4254f58801b9ee7db7bca5fa8aeefaa56b"}, @access.ref_map)
-  
+
     map = @access.tree_map['60f12f4254f58801b9ee7db7bca5fa8aeefaa56b']
     assert_equal 'Bilbo-Baggins.md',        map[0].path
     assert_equal '',                        map[0].dir
@@ -45,4 +44,16 @@ context "GitAccess" do
     entry = @access.tree_map['60f12f4254f58801b9ee7db7bca5fa8aeefaa56b'][0]
     assert_equal 'Bilbo-Baggins.md', entry.path
   end
+
+  test "cannot access commit from invalid ref" do
+    assert_nil @access.commit('foo')
+  end
+
+  test "cannot access sha from invalid ref" do
+    assert_nil @access.ref_to_sha('foo')
+  end
+
+  test "cannot access tree from invalid ref" do
+    assert_nil @access.tree('foo')
+  end
 end