Add NULL support to Client DER library

client/tests/der_tests.vala

@@ -180,6 +180,10 @@ void main(string[] args) {
 			test_encode(choice, expected);
 		});
 
+	Test.add_func("/encode/null", () => {
+			test_encode(new Der.Null(), { 0x05, 0x00 });
+		});
+
 	/*
 	 * Decoding
 	 */
@@ -289,5 +293,23 @@ void main(string[] args) {
 			test_utf8string_value("foo", choice.value);
 		});
 
+	Test.add_func("/decode/null", () => {
+			var bytes = new uint8[] { 0x05, 0x00 };
+			Der.Null @null;
+			try {
+				@null = decode(bytes) as Der.Null;
+			} catch (DecodeError err) {
+				Test.message("Decoding failed: %s", err.message);
+				Test.fail();
+				return;
+			}
+			if (@null == null) {
+				Test.message("Bytes were not decoded as a NULL");
+				Test.fail();
+				return;
+			}
+		});
+
+
 	Test.run();
 }