diff --git a/src/Executor/ExecutionResult.php b/src/Executor/ExecutionResult.php
index 7fc7523..8f78ef3 100644
--- a/src/Executor/ExecutionResult.php
+++ b/src/Executor/ExecutionResult.php
@@ -37,7 +37,11 @@ class ExecutionResult
      */
     public function toArray()
     {
-        $result = ['data' => $this->data];
+        $result = [];
+
+        if (null !== $this->data) {
+            $result['data'] = $this->data;
+        }
 
         if (!empty($this->errors)) {
             $result['errors'] = array_map(['GraphQL\Error', 'formatError'], $this->errors);
diff --git a/tests/Executor/ExecutionResultTest.php b/tests/Executor/ExecutionResultTest.php
index 1c942f7..68bff90 100644
--- a/tests/Executor/ExecutionResultTest.php
+++ b/tests/Executor/ExecutionResultTest.php
@@ -9,17 +9,17 @@ class ExecutionResultTest extends \PHPUnit_Framework_TestCase
     {
         $executionResult = new ExecutionResult();
 
-        $this->assertEquals(['data' => null], $executionResult->toArray());
+        $this->assertEquals([], $executionResult->toArray());
     }
 
     public function testToArrayExtensions()
     {
         $executionResult = new ExecutionResult(null, [], ['foo' => 'bar']);
 
-        $this->assertEquals(['data' => null, 'extensions' => ['foo' => 'bar']], $executionResult->toArray());
+        $this->assertEquals(['extensions' => ['foo' => 'bar']], $executionResult->toArray());
 
         $executionResult->extensions = ['bar' => 'foo'];
 
-        $this->assertEquals(['data' => null, 'extensions' => ['bar' => 'foo']], $executionResult->toArray());
+        $this->assertEquals(['extensions' => ['bar' => 'foo']], $executionResult->toArray());
     }
 }
diff --git a/tests/Executor/NonNullTest.php b/tests/Executor/NonNullTest.php
index b2cd3cd..c0b67ef 100644
--- a/tests/Executor/NonNullTest.php
+++ b/tests/Executor/NonNullTest.php
@@ -243,7 +243,6 @@ class NonNullTest extends \PHPUnit_Framework_TestCase
         ';
 
         $expected = [
-            'data' => null,
             'errors' => [
                 FormattedError::create($this->nonNullSyncError->getMessage(), [new SourceLocation(2, 17)])
             ]
@@ -259,7 +258,6 @@ class NonNullTest extends \PHPUnit_Framework_TestCase
         ';
 
         $expected = [
-            'data' => null,
             'errors' => [
                 FormattedError::create('Cannot return null for non-nullable field DataType.nonNullSync.', [new SourceLocation(2, 17)]),
             ]