Fields that are int types like Volume don't work with is, is not and crash with contains, not contains. Since the value set in the plugin is (probably) always a string, converting the field_data to a string (or unicode to prevent char like Japanese to crash). This way contains should also work correctly.
When encountering a rule with greater than and less than, the existing code should take care to convert back to an int already.
Fields that are int types like Volume don't work with is, is not and crash with contains, not contains. Since the value set in the plugin is (probably) always a string, converting the field_data to a string (or unicode to prevent char like Japanese to crash). This way contains should also work correctly.
When encountering a rule with greater than and less than, the existing code should take care to convert back to an int already.