title: SimpleSchema error: After filtering out keys not in the schema, your modifier is now empty
body: <p>I created new SimpleSchema for my collection. Collection definition &amp; schema:</p>
  
  <p><a href="https://gist.github.com/CandyOgre/c767032f34eeb78323becb3aa7ec83b3" rel="nofollow">GIST</a></p>
  
  <p>After calling this method from client:</p>
  
  <pre><code>export const setEventInvitationStatus = new ValidatedMethod({
   name: 'events.updateParticipantStatus',
  
   mixins: [LoggedInMixin],
  
   checkLoggedInError: {
    error: 'notLogged',
   },
  
   validate: new SimpleSchema({
    eventId: { type: String },
    inviteTo: { type: String },
    newStatus: { type: String },
   }).validator(),
  
   run({ eventId, inviteTo, newStatus }) {
    Events.update(
      {  '_id': eventId, 'participants.userId': inviteTo },
     {
      $set: { 'participants.$.inviteStatus': newStatus },
     });
   },
  });
  </code></pre>
  
  <p>I get this error:</p>
  
  <pre><code>Exception while invoking method 'events.updateParticipantStatus' { stack: 'Error: After filtering out keys not in the schema, your modifier is now empty\n    at [object Object].doValidate (packages/aldeed_collection2-core/lib/collection2.js:374:1)\n    at [object Object].Mongo.Collection.(anonymous function) [as update] (packages/aldeed_collection2-core/lib/collection2.js:173:1)\n    at [object Object].run (imports/api/events/server/methods.js:101:10)\n    at [object Object].LoggedInMixin.methodOptions.run (packages/tunifight:loggedin-mixin/loggedin-mixin.js:28:16)\n    at ValidatedMethod._execute (packages/mdg:validated-method/validated-method.js:93:12)\n    at [object Object].ValidatedMethod.connection.methods._connection$methods.(anonymous function) (packages/mdg:validated-method/validated-method.js:54:23)\n    at [object Object].methodMap.(anonymous function) (packages/meteorhacks_kadira/lib/hijack/wrap_session.js:164:1)\n    at maybeAuditArgumentChecks (packages/ddp-server/livedata_server.js:1704:12)\n    at packages/ddp-server/livedata_server.js:711:19\n    at [object Object]._.extend.withValue (packages/meteor/dynamics_nodejs.js:56:1)',
  </code></pre>
  
  <p>What I do wrong ?</p>