diff --git a/src/main/java/io/castle/client/internal/CastleApiImpl.java b/src/main/java/io/castle/client/internal/CastleApiImpl.java
index 3ffe2c8..d193a4d 100644
--- a/src/main/java/io/castle/client/internal/CastleApiImpl.java
+++ b/src/main/java/io/castle/client/internal/CastleApiImpl.java
@@ -336,6 +336,9 @@ public CastleResponse log(ImmutableMap<Object, Object> payload) {
 
     @Override
     public CastleResponse recover(String userId) {
+        Preconditions.checkNotNull(userId, "UserId can not be null");
+        Preconditions.checkArgument(!userId.isEmpty());
+
         RestApi restApi = configuration.getRestApiFactory().buildBackend();
         return restApi.put(String.format(Castle.URL_RECOVER, userId));
     }