title: Firebase Analytics Error Cannot create Value type with unsupported value
body: <p>I'm trying to log a few events, but the console is telling me there are errors. Here's a couple of events I'm trying to log:</p>
  
  <pre><code>Analytics.logEvent("workout_velocities", parameters: [
    "workout_uuid": UUID().uuidString,
    "speed": [
      "2018-02-22 07:46:37 +0000": -1,
      "2018-02-22 07:46:38 +0000": -1,
      "2018-02-22 07:46:39 +0000": -1
    ]
  ])
  </code></pre>
  
  <p>I get the following error message:</p>
  
  <pre><code>2018-02-21 23:52:42.480336-0800 RunManager[1878:1120392] 4.8.1 - [Firebase/Analytics][I-ACS035001] Cannot create Value type with unsupported value. The Value has to be NSNumber or NSString. Value: {
  "2018-02-22 07:46:37 +0000" = "-1";
  "2018-02-22 07:46:38 +0000" = "-1";
  "2018-02-22 07:46:39 +0000" = "-1";
  }
  2018-02-21 23:52:42.480414-0800 RunManager[1878:1120392] 4.8.1 -     [Firebase/Analytics][I-ACS016000] Event parameter value must be of type     NSString or NSNumber. Type: _TtGCs26_SwiftDeferredNSDictionarySSSi_
  </code></pre>