diff --git a/src/main/java/graphql/language/InputObjectTypeDefinition.java b/src/main/java/graphql/language/InputObjectTypeDefinition.java
index c2f414404..d54581409 100644
--- a/src/main/java/graphql/language/InputObjectTypeDefinition.java
+++ b/src/main/java/graphql/language/InputObjectTypeDefinition.java
@@ -1,14 +1,13 @@
 package graphql.language;
 
-
 import com.google.common.collect.ImmutableList;
 import graphql.Internal;
 import graphql.PublicApi;
 import graphql.collect.ImmutableKit;
+import graphql.util.FpKit;
 import graphql.util.TraversalControl;
 import graphql.util.TraverserContext;
 
-import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -75,10 +74,7 @@ public String getName() {
 
     @Override
     public List<Node> getChildren() {
-        List<Node> result = new ArrayList<>();
-        result.addAll(directives.getDirectives());
-        result.addAll(inputValueDefinitions);
-        return result;
+        return FpKit.concat(directives.getDirectives(), inputValueDefinitions);
     }
 
     @Override
diff --git a/src/main/java/graphql/language/SchemaDefinition.java b/src/main/java/graphql/language/SchemaDefinition.java
index 666decc46..931ef33c4 100644
--- a/src/main/java/graphql/language/SchemaDefinition.java
+++ b/src/main/java/graphql/language/SchemaDefinition.java
@@ -5,10 +5,10 @@
 import graphql.Internal;
 import graphql.PublicApi;
 import graphql.collect.ImmutableKit;
+import graphql.util.FpKit;
 import graphql.util.TraversalControl;
 import graphql.util.TraverserContext;
 
-import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -71,10 +71,7 @@ public Description getDescription() {
 
     @Override
     public List<Node> getChildren() {
-        List<Node> result = new ArrayList<>();
-        result.addAll(directives.getDirectives());
-        result.addAll(operationTypeDefinitions);
-        return result;
+        return FpKit.concat(directives.getDirectives(), operationTypeDefinitions);
     }
 
     @Override
diff --git a/src/main/java/graphql/language/UnionTypeDefinition.java b/src/main/java/graphql/language/UnionTypeDefinition.java
index c932c6390..9af502db8 100644
--- a/src/main/java/graphql/language/UnionTypeDefinition.java
+++ b/src/main/java/graphql/language/UnionTypeDefinition.java
@@ -5,10 +5,10 @@
 import graphql.Internal;
 import graphql.PublicApi;
 import graphql.collect.ImmutableKit;
+import graphql.util.FpKit;
 import graphql.util.TraversalControl;
 import graphql.util.TraverserContext;
 
-import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -95,10 +95,7 @@ public String getName() {
 
     @Override
     public List<Node> getChildren() {
-        List<Node> result = new ArrayList<>();
-        result.addAll(directives.getDirectives());
-        result.addAll(memberTypes);
-        return result;
+        return FpKit.concat(directives.getDirectives(), memberTypes);
     }
 
     @Override
diff --git a/src/main/java/graphql/util/FpKit.java b/src/main/java/graphql/util/FpKit.java
index f804a5497..b4bf6ca60 100644
--- a/src/main/java/graphql/util/FpKit.java
+++ b/src/main/java/graphql/util/FpKit.java
@@ -265,7 +265,7 @@ public static <T> List<T> concat(List<T> l, T t) {
      *
      * @return a <strong>new</strong> list composed of the two concatenated lists elements
      */
-    public static <T> List<T> concat(List<T> l1, List<T> l2) {
+    public static <T> List<T> concat(List<? extends T> l1, List<? extends T> l2) {
         List<T> l = new ArrayList<>(l1.size() + l2.size());
         l.addAll(l1);
         l.addAll(l2);