src/Composer/Json/JsonFile.php
public static function parseJson($json, $file = null)
    {
        if (null === $json) {
            return;
        }
        $data = json_decode($json, true);
        if (null === $data && JSON_ERROR_NONE !== json_last_error()) {
            self::validateSyntax($json, $file);
        }

        return $data;
    }
public static function parseJson($json, $file = null)
    {
        if (null === $json) {
            return;
        }
        $data = json_decode($json, true);
        if (null === $data && JSON_ERROR_NONE !== json_last_error()) {
            self::validateSyntax($json, $file);
        }

        return $data;
    }
Parses json string and returns hash.

@param string $json json string
@param string $file the json file

@return mixed