fix: 🐛 Fix fallbacking of locale to the code to prevent errors

perun-oidc-server/src/main/java/cz/muni/ics/openid/connect/config/JsonMessageSource.java

@@ -58,6 +58,8 @@ public JsonMessageSource(ConfigurationPropertiesBean config) {
 		this.config = config;
 	}
 
+
+
 	@Override
 	protected MessageFormat resolveCode(String code, Locale locale) {
 
@@ -73,7 +75,7 @@ protected MessageFormat resolveCode(String code, Locale locale) {
 
 		if (value == null) {
 			// if it's still null, return null
-			return null;
+			return new MessageFormat(code, locale);
 		} else {
 			// otherwise format the message
 			return new MessageFormat(value, locale);

perun-oidc-server/src/test/java/cz/muni/ics/openid/connect/config/TestJsonMessageSource.java

@@ -43,7 +43,8 @@ public void verifyWhenLocaleExists_canResolveCode() {
 
 	@Test
 	public void verifyWhenLocaleDoesNotExist_cannotResolveCode() {
+		String code = "test";
 		MessageFormat mf = jsonMessageSource.resolveCode("test", localeThatDoesNotHaveAFile);
-		assertNull(mf);
+		assertEquals(code, mf.toPattern());
 	}
 }