diff --git a/src/main/java/com/exaroton/api/request/billing/pools/CreditPoolRequest.java b/src/main/java/com/exaroton/api/request/billing/pools/CreditPoolRequest.java
index 90a87b7..a34b7ee 100644
--- a/src/main/java/com/exaroton/api/request/billing/pools/CreditPoolRequest.java
+++ b/src/main/java/com/exaroton/api/request/billing/pools/CreditPoolRequest.java
@@ -3,13 +3,14 @@
 import com.exaroton.api.APIRequest;
 import com.exaroton.api.ExarotonClient;
 import com.exaroton.api.billing.pools.CreditPool;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.HashMap;
 
 public abstract class CreditPoolRequest<T> extends APIRequest<T> {
     private final String poolId;
 
-    public CreditPoolRequest(ExarotonClient client, String id) {
+    public CreditPoolRequest(@NotNull ExarotonClient client, @NotNull String id) {
         super(client);
         this.poolId = id;
     }
diff --git a/src/test/java/APIClientTest.java b/src/test/java/APIClientTest.java
index bae00ef..c5d0bc1 100644
--- a/src/test/java/APIClientTest.java
+++ b/src/test/java/APIClientTest.java
@@ -1,8 +1,9 @@
 import com.exaroton.api.ExarotonClient;
 import com.exaroton.api.server.Server;
+import org.jetbrains.annotations.NotNull;
 
 public abstract class APIClientTest {
-    protected static final String TEST_SERVER_ID = System.getenv("EXAROTON_TEST_SERVER");
-    protected final ExarotonClient client = new ExarotonClient(System.getenv("EXAROTON_API_TOKEN"));
-    protected final Server server = client.getServer(TEST_SERVER_ID);
+    protected static final @NotNull String TEST_SERVER_ID = System.getenv("EXAROTON_TEST_SERVER");
+    protected final @NotNull ExarotonClient client = new ExarotonClient(System.getenv("EXAROTON_API_TOKEN"));
+    protected final @NotNull Server server = client.getServer(TEST_SERVER_ID);
 }
diff --git a/src/test/java/CreditPoolsTest.java b/src/test/java/CreditPoolsTest.java
index 224f5ec..905062c 100644
--- a/src/test/java/CreditPoolsTest.java
+++ b/src/test/java/CreditPoolsTest.java
@@ -2,6 +2,7 @@
 import com.exaroton.api.billing.pools.CreditPool;
 import com.exaroton.api.billing.pools.CreditPoolMember;
 import com.exaroton.api.server.Server;
+import org.jetbrains.annotations.NotNull;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
@@ -9,7 +10,7 @@
 import java.util.Optional;
 
 public class CreditPoolsTest extends APIClientTest {
-    private static final String TEST_POOL_ID = System.getenv("EXAROTON_TEST_POOL");
+    private static final @NotNull String TEST_POOL_ID = System.getenv("EXAROTON_TEST_POOL");
 
     @Test
     public void testGetCreditPools() throws APIException {