Minus breaks extract_json_value and anything dependent on json_to_xml

[GoogleCodeExporter]

Which version of common_schema are you using? (2.2)

Which component is failing?  json_to_xml and anything dependent on it like 
extract_json_value

What is the expected output? expected -5 got null

Can you provide with sample data?
select common_schema.extract_json_value('{"grade":"-5"}', "grade"); // Got NULL 
expected -5
select common_schema.extract_json_value('{"grade":"5"}', "grade"); // Works, 
got 5 Expected 5

(As of version 1.1), please provide output of
mysql> SELECT * FROM common_schema.status;
+---------------+---------+----------+---------------------+-----------------+--
-------------------------+------------------------------------+-----------------
--------------------+-------------------------+-----------------------+
| project_name  | version | revision | install_time        | install_success | 
base_components_installed | innodb_plugin_components_installed | 
percona_server_components_installed | install_mysql_version   | 
install_sql_mode      |
+---------------+---------+----------+---------------------+-----------------+--
-------------------------+------------------------------------+-----------------
--------------------+-------------------------+-----------------------+
| common_schema | 2.2     | 523      | 2014-12-12 13:32:41 | 1               | 
1                         | 1                                  | 0              
                     | 5.5.40-0ubuntu0.14.04.1 | NO_AUTO_VALUE_ON_ZERO |
+---------------+---------+----------+---------------------+-----------------+--
-------------------------+------------------------------------+-----------------
--------------------+-------------------------+-----------------------+

Original issue reported on code.google.com by [email protected] on 15 Dec 2014 at 4:04