deal with empty initial commit

lib/grit/commit.rb

@@ -156,8 +156,12 @@ module Grit
 
     def diffs
       if parents.empty?
-        diff = @repo.git.show({:full_index => true, :pretty => 'raw'}, @id) 
-        diff = diff.sub(/.+?(diff --git a)/m, '\1')
+        diff = @repo.git.show({:full_index => true, :pretty => 'raw'}, @id)
+        if diff =~ /diff --git a/
+          diff = diff.sub(/.+?(diff --git a)/m, '\1')
+        else
+          diff = ''
+        end
         Diff.list_from_string(@repo, diff)
       else
         self.class.diff(@repo, parents.first.id, @id) 

test/fixtures/show_empty_commit

@@ -0,0 +1,6 @@
+commit 1e3824339762bd48316fe87bfafc853732d43264
+tree 4b825dc642cb6eb9a060e54bf8d69288fbee4904
+author Tom Preston-Werner <tom@mojombo.com> 1157392833 +0000
+committer Tom Preston-Werner <tom@mojombo.com> 1157392833 +0000
+
+    initial directory structure

test/test_commit.rb

@@ -98,6 +98,18 @@ class TestCommit < Test::Unit::TestCase
     assert_equal true, diffs[5].new_file
   end
   
+  def test_diffs_on_initial_import_with_empty_commit
+    Git.any_instance.expects(:show).with(
+      {:full_index => true, :pretty => 'raw'}, 
+      '634396b2f541a9f2d58b00be1a07f0c358b999b3'
+    ).returns(fixture('show_empty_commit'))
+    
+    @c = Commit.create(@r, :id => '634396b2f541a9f2d58b00be1a07f0c358b999b3')
+    diffs = @c.diffs
+    
+    assert_equal [], diffs
+  end
+  
   # to_s
   
   def test_to_s