rules block: filter: Panic: interface conversion: interface {} is int, not string

[saimikiry]

Hi, devs! I found a problem similar to this one: #757

Using the value 00 as a filter will result in a panic:

To reproduce the issue, you can modify the default configuration file as follows (filter: 00):

...

- description: "Search LDAP to create readers, writers and owners."
  ldapsearch:
    base: cn=users,dc=bridoulou,dc=fr
    filter: 00
  role:
    name: '{member.cn}'
    options: LOGIN
    parent: "{cn}"