add support for NullValue

src/Language/AST/Node.php

@@ -31,6 +31,7 @@ abstract class Node
 
     // Values
 
+    const NULL = 'NullValue';
     const INT = 'IntValue';
     const FLOAT = 'FloatValue';
     const STRING = 'StringValue';

src/Language/AST/NullValue.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace GraphQL\Language\AST;
+
+class NullValue extends Node implements Value
+{
+    public $kind = Node::NULL;
+
+    /**
+     * @var null
+     */
+    protected $value = null;
+
+    /**
+     * NullValue constructor.
+     *
+     * @param string $value
+     * @param null   $loc
+     */
+    public function __construct($loc = null)
+    {
+        $this->loc = $loc;
+    }
+
+    /**
+     * @return null
+     */
+    public function getValue()
+    {
+        return $this->value;
+    }
+}

src/Language/AST/Value.php

@@ -10,6 +10,7 @@
 | EnumValue
 | ListValue
 | ObjectValue
+| NullValue
  */
 interface Value
 {

src/Language/Parser.php

@@ -27,6 +27,7 @@
 use GraphQL\Language\AST\Name;
 use GraphQL\Language\AST\NamedType;
 use GraphQL\Language\AST\NonNullType;
+use GraphQL\Language\AST\NullValue;
 use GraphQL\Language\AST\ObjectField;
 use GraphQL\Language\AST\ObjectTypeDefinition;
 use GraphQL\Language\AST\ObjectValue;
@@ -655,14 +656,18 @@ function parseValueLiteral($isConst)
                         'value' => $token->value === 'true',
                         'loc' => $this->loc($token)
                     ]);
-                } else if ($token->value !== 'null') {
+                } else if ($token->value === 'null') {
+                    $this->lexer->advance();
+                    return new NullValue(
+                        $this->loc($token)
+                    );
+                } else {
                     $this->lexer->advance();
                     return new EnumValue([
                         'value' => $token->value,
                         'loc' => $this->loc($token)
                     ]);
                 }
-                break;
 
             case Token::DOLLAR:
                 if (!$isConst) {

tests/Language/ParserTest.php

@@ -9,6 +9,7 @@
 use GraphQL\Language\AST\Name;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\OperationDefinition;
+use GraphQL\Language\AST\NullValue;
 use GraphQL\Language\AST\SelectionSet;
 use GraphQL\Language\AST\StringValue;
 use GraphQL\Language\Parser;
@@ -112,10 +113,26 @@ public function testDoesNotAcceptFragmentSpreadOfOn()
     /**
      * @it does not allow null as value
      */
-    public function testDoesNotAllowNullAsValue()
+    public function testAllowsNullAsValue()
     {
-        $this->setExpectedException('GraphQL\Error\SyntaxError', 'Syntax Error GraphQL (1:39) Unexpected Name "null"');
-        Parser::parse('{ fieldWithNullableStringInput(input: null) }');
+        $expected = new SelectionSet([
+            'selections' => [
+                new Field([
+                    'name' => new Name(['value' => 'fieldWithNullableStringInput']),
+                    'arguments' => [
+                        new Argument([
+                            'name' => new Name(['value' => 'input']),
+                            'value' => new NullValue()
+                        ])
+                    ],
+                    'directives' => []
+                ])
+            ]
+        ]);
+
+        $result = Parser::parse('{ fieldWithNullableStringInput(input: null) }', ['noLocation' => true]);
+
+        $this->assertEquals($expected, $result->definitions[0]->selectionSet);
     }
 
     /**