allowing null values to be passed into DefaultExecutionStrategyProvider because graphql-java handles null values and uses defaults when null execution strategies are given, so there is no longer a need to have default values set in this library

Author: bsara

graphql-java-kickstart/src/main/java/graphql/kickstart/execution/config/DefaultExecutionStrategyProvider.java

@@ -1,8 +1,6 @@
 package graphql.kickstart.execution.config;
 
-import graphql.execution.AsyncExecutionStrategy;
 import graphql.execution.ExecutionStrategy;
-import graphql.execution.SubscriptionExecutionStrategy;
 
 /**
  * @author Andrew Potter
@@ -18,19 +16,14 @@ public DefaultExecutionStrategyProvider() {
   }
 
   public DefaultExecutionStrategyProvider(ExecutionStrategy executionStrategy) {
-    this(executionStrategy, null, null);
+    this(executionStrategy, executionStrategy, null);
   }
 
   public DefaultExecutionStrategyProvider(ExecutionStrategy queryExecutionStrategy,
       ExecutionStrategy mutationExecutionStrategy, ExecutionStrategy subscriptionExecutionStrategy) {
-    this.queryExecutionStrategy = defaultIfNull(queryExecutionStrategy, new AsyncExecutionStrategy());
-    this.mutationExecutionStrategy = defaultIfNull(mutationExecutionStrategy, this.queryExecutionStrategy);
-    this.subscriptionExecutionStrategy = defaultIfNull(subscriptionExecutionStrategy,
-        new SubscriptionExecutionStrategy());
-  }
-
-  private ExecutionStrategy defaultIfNull(ExecutionStrategy executionStrategy, ExecutionStrategy defaultStrategy) {
-    return executionStrategy != null ? executionStrategy : defaultStrategy;
+    this.queryExecutionStrategy = queryExecutionStrategy;
+    this.mutationExecutionStrategy = mutationExecutionStrategy;
+    this.subscriptionExecutionStrategy = subscriptionExecutionStrategy;
   }
 
   @Override