diff --git a/routers/api/v1/repo/repo.go b/routers/api/v1/repo/repo.go
index eb1bef5a7..2e551ef83 100644
--- a/routers/api/v1/repo/repo.go
+++ b/routers/api/v1/repo/repo.go
@@ -1152,8 +1152,13 @@ func PrepareCompareDiff(
 		ctx.ServerError("GetDiffRange", err)
 		return false
 	}
-	ctx.Data["Diff"] = diff
-	ctx.Data["DiffNotAvailable"] = diff.NumFiles == 0
+	if diff.NumFiles == 0 {
+		ctx.Data["Diff"] = nil
+		ctx.Data["DiffNotAvailable"] = true
+	} else {
+		ctx.Data["Diff"] = diff
+		ctx.Data["DiffNotAvailable"] = false
+	}
 
 	return false
 }