diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/util/IdentifierValidator.java b/client-api/src/main/java/ru/dragonestia/picker/api/util/IdentifierValidator.java
index 596ea6a..4d5ed83 100644
--- a/client-api/src/main/java/ru/dragonestia/picker/api/util/IdentifierValidator.java
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/util/IdentifierValidator.java
@@ -1,18 +1,20 @@
 package ru.dragonestia.picker.api.util;
 
+import org.jetbrains.annotations.NotNull;
+
 public class IdentifierValidator {
 
     private IdentifierValidator() {}
 
-    public static boolean forNode(String nodeId) {
+    public static boolean forNode(@NotNull String nodeId) {
         return nodeId.matches("^(?!-)[a-z\\d-]{0,31}[a-z\\d](?!-)$");
     }
 
-    public static boolean forRoom(String roomId) {
+    public static boolean forRoom(@NotNull String roomId) {
         return roomId.matches("^(?!-)[a-z\\d-]{0,31}[a-z\\d](?!-)$");
     }
 
-    public static boolean forUser(String username) {
+    public static boolean forUser(@NotNull String username) {
         return username.matches("^[aA-zZ\\d-.\\s:@_;]{1,64}$");
     }
 }