diff --git a/src/main/java/com/gw2auth/oauth2/server/util/QueryParam.java b/src/main/java/com/gw2auth/oauth2/server/util/QueryParam.java
index e581e83..4b7ea06 100644
--- a/src/main/java/com/gw2auth/oauth2/server/util/QueryParam.java
+++ b/src/main/java/com/gw2auth/oauth2/server/util/QueryParam.java
@@ -1,24 +1,11 @@
 package com.gw2auth.oauth2.server.util;
 
-import org.jspecify.annotations.Nullable;
-
 import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
-import java.util.Optional;
 
-public interface QueryParam {
+public sealed interface QueryParam {
 
     String name();
-    @Nullable String value();
-    boolean hasValue();
-
-    default Optional<String> optionalValue() {
-        if (hasValue()) {
-            return Optional.of(value());
-        } else {
-            return Optional.empty();
-        }
-    }
 
     static QueryParam parse(String rawPair) {
         final String[] pair = Utils.split(rawPair, "=", 2).map((part) -> URLDecoder.decode(part, StandardCharsets.UTF_8)).toArray(String[]::new);
@@ -30,24 +17,7 @@ static QueryParam parse(String rawPair) {
         }
     }
 
-    record QueryParamWithValue(String name, String value) implements QueryParam {
+    record QueryParamWithValue(String name, String value) implements QueryParam {}
 
-        @Override
-        public boolean hasValue() {
-            return true;
-        }
-    }
-
-    record QueryParamWithoutValue(String name) implements QueryParam {
-
-        @Override
-        public @Nullable String value() {
-            return null;
-        }
-
-        @Override
-        public boolean hasValue() {
-            return false;
-        }
-    }
+    record QueryParamWithoutValue(String name) implements QueryParam {}
 }
diff --git a/src/test/java/com/gw2auth/oauth2/server/Gw2AuthLoginExtension.java b/src/test/java/com/gw2auth/oauth2/server/Gw2AuthLoginExtension.java
index 6b6dc6a..5a74a19 100644
--- a/src/test/java/com/gw2auth/oauth2/server/Gw2AuthLoginExtension.java
+++ b/src/test/java/com/gw2auth/oauth2/server/Gw2AuthLoginExtension.java
@@ -164,9 +164,10 @@ private ResultActions loginInternal(SessionHandle sessionHandle, String loginURL
 
         final String location = Objects.requireNonNull(result.getResponse().getRedirectedUrl());
         final String state = Utils.parseQuery(new URI(location).parseServerAuthority().getRawQuery())
-                .filter(QueryParam::hasValue)
+                .map(queryParam -> queryParam instanceof QueryParam.QueryParamWithValue qpwv ? qpwv : null)
+                .filter(Objects::nonNull)
                 .filter((queryParam) -> queryParam.name().equals(OAuth2ParameterNames.STATE))
-                .map(QueryParam::value)
+                .map(QueryParam.QueryParamWithValue::value)
                 .findFirst()
                 .orElseThrow();
 
diff --git a/src/test/java/com/gw2auth/oauth2/server/Matchers.java b/src/test/java/com/gw2auth/oauth2/server/Matchers.java
index 2c934f5..63058a5 100644
--- a/src/test/java/com/gw2auth/oauth2/server/Matchers.java
+++ b/src/test/java/com/gw2auth/oauth2/server/Matchers.java
@@ -1,5 +1,6 @@
 package com.gw2auth.oauth2.server;
 
+import com.gw2auth.oauth2.server.util.QueryParam.QueryParamWithValue;
 import com.gw2auth.oauth2.server.util.Utils;
 import org.hamcrest.Description;
 import org.hamcrest.Matcher;
@@ -35,8 +36,8 @@ public static Matcher<String> asUri(Matcher<? super UriComponents> matcher) {
                     .fragment(uri.getFragment());
 
             Utils.parseQuery(uri.getRawQuery()).forEach((queryParam) -> {
-                if (queryParam.hasValue()) {
-                    builder.queryParam(queryParam.name(), queryParam.value());
+                if (queryParam instanceof QueryParamWithValue(String name, String value)) {
+                    builder.queryParam(name, value);
                 } else {
                     builder.queryParam(queryParam.name());
                 }
diff --git a/src/test/java/com/gw2auth/oauth2/server/oauth2/OAuth2ServerTest.java b/src/test/java/com/gw2auth/oauth2/server/oauth2/OAuth2ServerTest.java
index 18da959..e0340bc 100644
--- a/src/test/java/com/gw2auth/oauth2/server/oauth2/OAuth2ServerTest.java
+++ b/src/test/java/com/gw2auth/oauth2/server/oauth2/OAuth2ServerTest.java
@@ -30,6 +30,7 @@
 import com.gw2auth.oauth2.server.service.application.client.account.ApplicationClientAccount;
 import com.gw2auth.oauth2.server.service.application.client.authorization.ApplicationClientAuthorizationServiceImpl;
 import com.gw2auth.oauth2.server.util.QueryParam;
+import com.gw2auth.oauth2.server.util.QueryParam.QueryParamWithValue;
 import com.gw2auth.oauth2.server.util.Utils;
 import com.nimbusds.jwt.JWT;
 import com.nimbusds.jwt.JWTParser;
@@ -1328,9 +1329,10 @@ public void consentSubmitWithUnexpectedGW2APIException(SessionHandle sessionHand
 
         // retrieve the initial access and refresh token
         final String codeParam = Utils.parseQuery(URI.create(Objects.requireNonNull(result.getResponse().getRedirectedUrl())).getRawQuery())
-                .filter(QueryParam::hasValue)
+                .map(queryParam -> queryParam instanceof QueryParamWithValue qpwv ? qpwv : null)
+                .filter(Objects::nonNull)
                 .filter((queryParam) -> queryParam.name().equals(OAuth2ParameterNames.CODE))
-                .map(QueryParam::value)
+                .map(QueryParamWithValue::value)
                 .findFirst()
                 .orElse(null);
 
@@ -1499,8 +1501,9 @@ public void consentSubmitWithLessScopesThanRequested(SessionHandle sessionHandle
 
         // read request information from redirected uri
         final Map<String, String> params = Utils.parseQuery(URI.create(result.getResponse().getRedirectedUrl()).getRawQuery())
-                .filter(QueryParam::hasValue)
-                .collect(Collectors.toMap(QueryParam::name, QueryParam::value));
+                .map(queryParam -> queryParam instanceof QueryParamWithValue qpwv ? qpwv : null)
+                .filter(Objects::nonNull)
+                .collect(Collectors.toMap(QueryParam::name, QueryParamWithValue::value));
 
         assertTrue(params.containsKey(OAuth2ParameterNames.CLIENT_ID));
         assertTrue(params.containsKey(OAuth2ParameterNames.STATE));
@@ -2413,9 +2416,10 @@ private ResultActions performRetrieveTokenByCode(ApplicationClient applicationCl
 
     private ResultActions performRetrieveTokenByCode(ApplicationClient applicationClient, String clientSecret, String redirectUri, URI redirectedURI, Map<String, String> subtokenByGw2ApiToken, Set<Gw2ApiPermission> expectedGw2ApiPermissions) throws Exception {
         final String codeParam = Utils.parseQuery(redirectedURI.getRawQuery())
-                .filter(QueryParam::hasValue)
+                .map(queryParam -> queryParam instanceof QueryParamWithValue qpwv ? qpwv : null)
+                .filter(Objects::nonNull)
                 .filter((queryParam) -> queryParam.name().equals(OAuth2ParameterNames.CODE))
-                .map(QueryParam::value)
+                .map(QueryParamWithValue::value)
                 .findFirst()
                 .orElse(null);
 
@@ -2589,8 +2593,9 @@ private ResultActions performSubmitConsent(SessionHandle sessionHandle,
 
         // read request information from redirected uri
         final Map<String, String> params = Utils.parseQuery(redirectedURI.getRawQuery())
-                .filter(QueryParam::hasValue)
-                .collect(Collectors.toMap(QueryParam::name, QueryParam::value));
+                .map(queryParam -> queryParam instanceof QueryParam.QueryParamWithValue qpwv ? qpwv : null)
+                .filter(Objects::nonNull)
+                .collect(Collectors.toMap(QueryParam::name, QueryParamWithValue::value));
 
         assertTrue(params.containsKey(OAuth2ParameterNames.CLIENT_ID));
         assertTrue(params.containsKey(OAuth2ParameterNames.STATE));