Expand {} into a new line before manipulating json, fixes #1481

src/Composer/Json/JsonManipulator.php

@@ -30,7 +30,7 @@ class JsonManipulator
             throw new \InvalidArgumentException('The json file must be an object ({})');
         }
         $this->newline = false !== strpos("\r\n", $contents) ? "\r\n": "\n";
-        $this->contents = $contents;
+        $this->contents = $contents === '{}' ? '{' . $this->newline . '}' : $contents;
         $this->detectIndenting();
     }
 

tests/Composer/Test/Json/JsonManipulatorTest.php

@@ -30,8 +30,7 @@ class JsonManipulatorTest extends \PHPUnit_Framework_TestCase
     {
         return array(
             array(
-                '{
+                '{}',
-}',
                 'require',
                 'vendor/baz',
                 'qux',