user_filter keyword is not working in gitlab ldap EE edition

I am using user_filter in gitlab EE but it's not working.. gitlab_rails['ldap_servers'] = YAML.load <<-'EOS' main: # 'main' is the GitLab 'provider ID' of this LDAP server label: 'GitLab AD' host: '***' #_your_ldap_server port: 389 uid: 'sAMAccountName' bind_dn: 'CN=GitLab AD,CN=Managed Service Accounts,OU=UserAccounts,DC=NAPROD,DC=wavesco,DC=com'#_the_full_dn_of_the_user_you_will_bind_with password: '' encryption: 'plain' # "start_tls" or "simple_tls" or "plain" verify_certificates: true active_directory: true base: 'DC=NAPROD,DC=wavesco,DC=com' user_filter : '' group_base: '' admin_group: 'GP-APP-GITLAB'

when i am using user_filter it gives the error "There was an error running gitlab-ctl reconfigure:(): found character that cannot start any token while scanning for the next token at line 12 column 1"

please suggest me