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Add a valid url in the mobilecssurlfield

Call the get_siteinfo WS function, in the result you will notice that mobilecssurl field is empty:

{"sitename":"XXXX","username":"student01","firstname":"Student","lastname":"Demo","fullname":"Student Demo","lang":"en","userid":3,"siteurl":"http:\/\/xxxx\/moodle24","userpictureurl":"http:\/\/xxxx\/moodle24\/pluginfile.php\/19\/user\/icon\/f1","functions":[

{"name":"moodle_enrol_get_users_courses","version":"2012120300.06"}

,

{"name":"moodle_enrol_get_enrolled_users","version":"2012120300.06"}

,

{"name":"moodle_user_get_users_by_id","version":"2012120300.06"}

,

{"name":"moodle_webservice_get_siteinfo","version":"2012120300.06"}

,

{"name":"moodle_notes_create_notes","version":"2012120300.06"}

,

{"name":"moodle_user_get_course_participants_by_id","version":"2012120300.06"}

,

{"name":"moodle_user_get_users_by_courseid","version":"2012120300.06"}

,

{"name":"moodle_message_send_instantmessages","version":"2012120300.06"}

,

{"name":"core_course_get_contents","version":"2012120300.06"}

,

{"name":"core_get_component_strings","version":"2012120300.06"}

],"downloadfiles":1,"release":"2.4+ (Build: 20121230)","version":"2012120300.06","mobilecssurl":""}