[libgit2-glib] ggit-diff-similarity-metric.c: Fix return annotations

[Igor Gnatenko <ignatenko src gnome org>]

commit 738adaa908687e5004ecb4529632949a0e9dfb5d
Author: Brian C. Lane <bcl redhat com>
Date:   Wed Aug 30 16:39:36 2017 -0700

    ggit-diff-similarity-metric.c: Fix return annotations
    
    Add (nullable) as needed.

 libgit2-glib/ggit-diff-similarity-metric.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgit2-glib/ggit-diff-similarity-metric.c b/libgit2-glib/ggit-diff-similarity-metric.c
index cf454c5..accc7c9 100644
--- a/libgit2-glib/ggit-diff-similarity-metric.c
+++ b/libgit2-glib/ggit-diff-similarity-metric.c
@@ -53,7 +53,7 @@ _ggit_diff_similarity_metric_get_similarity_metric (GgitDiffSimilarityMetric *me
  *
  * Copies @metric into a newly allocated #GgitDiffSimilarityMetric.
  *
- * Returns: (transfer full): a newly allocated #GgitDiffSimilarityMetric.
+ * Returns: (transfer full) (nullable): a newly allocated #GgitDiffSimilarityMetric or %NULL.
  */
 GgitDiffSimilarityMetric *
 ggit_diff_similarity_metric_copy (GgitDiffSimilarityMetric *metric)