codegen: Check param for null before using it

Regression of 5490b0b21a4089d803d51c91311430d60d266f7b

This caused criticals like:

  vala_get_ccode_array_length: assertion 'node != NULL' failed

See https://gitlab.gnome.org/GNOME/vala/issues/929

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/methods/varargs-ref.vala b/tests/methods/varargs-ref.vala
new file mode 100644
index 000000000..9c3f5fa74
--- /dev/null
+++ b/tests/methods/varargs-ref.vala
@@ -0,0 +1,14 @@
+void set_foo_varg (string s, ...) {
+	var args = va_list ();
+	string** ref_s1 = args.arg ();
+	*ref_s1 = "bar";
+	string** ref_s2 = args.arg ();
+	*ref_s2 = "manam";
+}
+
+void main () {
+	unowned string bar = "", manam = "";
+	set_foo_varg ("foo", ref bar, ref manam);
+	assert (bar == "bar");
+	assert (manam == "manam");
+}