refspec: introduce git_refspec__serialize()

src/refspec.c

@@ -225,3 +225,14 @@ int git_refspec_transform_l(git_buf *out, const git_refspec *spec, const char *n
 	return refspec_transform(out, spec->dst, spec->src, name);
 }
 
+int git_refspec__serialize(git_buf *out, const git_refspec *refspec)
+{
+	if (refspec->force)
+		git_buf_putc(out, '+');
+
+	git_buf_printf(out, "%s:%s",
+		refspec->src != NULL ? refspec->src : "",
+		refspec->dst != NULL ? refspec->dst : "");
+
+	return git_buf_oom(out) == false;
+}

src/refspec.h

@@ -51,4 +51,6 @@ int git_refspec_transform_r(git_buf *out, const git_refspec *spec, const char *n
  */
 int git_refspec_transform_l(git_buf *out, const git_refspec *spec, const char *name);
 
+int git_refspec__serialize(git_buf *out, const git_refspec *refspec);
+
 #endif

src/remote.c

@@ -237,17 +237,14 @@ static int update_config_refspec(
 	if (refspec->src == NULL || refspec->dst == NULL)
 		return 0;
 
-	git_buf_printf(
+	if (git_buf_printf(
 		&name,
 		"remote.%s.%s",
 		remote_name,
-		git_direction == GIT_DIR_FETCH ? "fetch" : "push");
+		git_direction == GIT_DIR_FETCH ? "fetch" : "push") < 0)
+			goto cleanup;
 
-	if (refspec->force)
-		git_buf_putc(&value, '+');
-	git_buf_printf(&value, "%s:%s", refspec->src, refspec->dst);
-	
-	if (git_buf_oom(&name) || git_buf_oom(&value))
+	if (git_refspec__serialize(&value, refspec) < 0)
 		goto cleanup;
 
 	error = git_config_set_string(