Added constructor validations to prevent NPEs

Author: artem-v

tokens/src/main/java/io/scalecube/security/tokens/jwt/JsonwebtokenResolver.java

@@ -3,6 +3,7 @@
 import io.jsonwebtoken.Jwts;
 import io.jsonwebtoken.Locator;
 import java.security.Key;
+import java.util.Objects;
 import java.util.concurrent.CompletableFuture;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -14,7 +15,7 @@ public class JsonwebtokenResolver implements JwtTokenResolver {
   private final Locator<Key> keyLocator;
 
   public JsonwebtokenResolver(Locator<Key> keyLocator) {
-    this.keyLocator = keyLocator;
+    this.keyLocator = Objects.requireNonNull(keyLocator, "keyLocator");
   }
 
   @Override

tokens/src/main/java/io/scalecube/security/tokens/jwt/JwksKeyLocator.java

@@ -25,6 +25,7 @@
 import java.time.Duration;
 import java.util.Base64;
 import java.util.Map;
+import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.locks.ReentrantLock;
 
@@ -41,9 +42,9 @@ public class JwksKeyLocator extends LocatorAdapter<Key> {
   private final ReentrantLock cleanupLock = new ReentrantLock();
 
   private JwksKeyLocator(Builder builder) {
-    this.jwksUri = builder.jwksUri;
-    this.connectTimeout = builder.connectTimeout;
-    this.requestTimeout = builder.requestTimeout;
+    this.jwksUri = Objects.requireNonNull(builder.jwksUri, "jwksUri");
+    this.connectTimeout = Objects.requireNonNull(builder.connectTimeout, "connectTimeout");
+    this.requestTimeout = Objects.requireNonNull(builder.requestTimeout, "requestTimeout");
     this.keyTtl = builder.keyTtl;
   }