Issue-13: Fixed issue that prevented null arguments from getting sets in query string

Author: mghoneimy

src/Query.php

@@ -189,7 +189,7 @@ protected function constructArguments(): string
  }
 
  // Convert argument values to graphql string literal equivalent
- if (is_scalar($value)) {
+ if (is_scalar($value) || $value === null) {
  // Convert scalar value to its literal in graphql
  $value = StringLiteralFormatter::formatValueForRHS($value);
  } elseif (is_array($value)) {

tests/QueryTest.php

@@ -353,6 +353,31 @@ public function testBooleanArgumentValue(Query $query)
  return $query;
  }
 
+ /**
+ * @depends clone testEmptyArguments
+ *
+ * @covers \GraphQL\Query::setArguments
+ * @covers \GraphQL\Query::constructArguments
+ *
+ * @param Query $query
+ *
+ * @return Query
+ */
+ public function testNullArgumentValue(Query $query)
+ {
+ $query->setArguments(['arg1' => null]);
+ $this->assertEquals(
+ "query {
+Object(arg1: null) {
+
+}
+}"
+ , (string) $query
+ );
+
+ return $query;
+ }
+
  /**
  * @depends clone testEmptyArguments
  *