PermissionsEX error

i have this eror: [ERROR] .... [PermissionsEX] [ERROR] .... null and i dont know how too fix it maybe you guys can help me out

Code:

groups:
 member:
    options:
      default: true
      prefix: '&7[Member]&f '
    permissions:
    - modifyworld.*
    - essentials.afk.use
    - essentials.compass
    - essentials.delhome
    - essentials.sethome
    - essentials.sethome.bed
    - essentials.sethome.multiple
    - essentials.depth
    - essentials.getpos.use
    - essentials.home.use
    - essentials.tpa
    - essentials.tpaccept
    - essentials.tpahere
    - essentials.tpdeny
    - essentials.warp.use
    - essentials.whois
    - essentials.msg
    - essentials.reply
    - essentials.spawn
    - minecraft.command.kill
    - minecraft.command.list
    - minecraft.command.seed
    - minecraft.command.tell
    - essentials.realname
    - essentials.kit.use
    - minecraft.command.help
 helper:
      prefix: '§a[Helper]&f '
        default: false
   permissions:
   - essentials.kick
   - essentials.kick.notify
   - essentials.mute
   - essentials.invsee
  dev:
    options:
      default: false
      prefix: '&9[dev&f]'
    permissions:
    -  (*)