diff --git a/build.gradle b/build.gradle
index 38b013f..84a3cfd 100644
--- a/build.gradle
+++ b/build.gradle
@@ -39,7 +39,7 @@ subprojects {
     group = 'com.graphql-java'
 
     ext {
-        graphqlJavaVersion = "12.0"
+        graphqlJavaVersion = "15.0"
         springVersion = "5.1.2.RELEASE"
         springBootVersion = "2.1.0.RELEASE"
         jacksonVersion = "2.9.6"
diff --git a/graphql-java-spring-webflux/src/main/java/graphql/spring/web/reactive/GraphQLInvocationData.java b/graphql-java-spring-webflux/src/main/java/graphql/spring/web/reactive/GraphQLInvocationData.java
index 35fc469..7697e39 100644
--- a/graphql-java-spring-webflux/src/main/java/graphql/spring/web/reactive/GraphQLInvocationData.java
+++ b/graphql-java-spring-webflux/src/main/java/graphql/spring/web/reactive/GraphQLInvocationData.java
@@ -14,7 +14,7 @@ public class GraphQLInvocationData {
     private final Map<String, Object> variables;
 
     public GraphQLInvocationData(String query, String operationName, Map<String, Object> variables) {
-        this.query = Assert.assertNotNull(query, "query must be provided");
+        this.query = Assert.assertNotNull(query, () -> "query must be provided");
         this.operationName = operationName;
         this.variables = variables != null ? variables : Collections.emptyMap();
     }
diff --git a/graphql-java-spring-webmvc/src/main/java/graphql/spring/web/servlet/GraphQLInvocationData.java b/graphql-java-spring-webmvc/src/main/java/graphql/spring/web/servlet/GraphQLInvocationData.java
index 43806b6..232d882 100644
--- a/graphql-java-spring-webmvc/src/main/java/graphql/spring/web/servlet/GraphQLInvocationData.java
+++ b/graphql-java-spring-webmvc/src/main/java/graphql/spring/web/servlet/GraphQLInvocationData.java
@@ -14,7 +14,7 @@ public class GraphQLInvocationData {
     private final Map<String, Object> variables;
 
     public GraphQLInvocationData(String query, String operationName, Map<String, Object> variables) {
-        this.query = Assert.assertNotNull(query, "query must be provided");
+        this.query = Assert.assertNotNull(query, () -> "query must be provided");
         this.operationName = operationName;
         this.variables = variables != null ? variables : Collections.emptyMap();
     }