title: Microsoft Graph API query failing with provided filter
body: <p>In my .NET application, I'm trying to get users from Azure AD B2C using Microsoft Graph API. I also want to filter these users based on a custom user attribute.</p>
  
  <p>I've built this URL</p>
  
  <pre><code>https://graph.microsoft.com/v1.0/users?$select=extension_{Id}_lastUpdatedDate&amp;$filter=extension_{Id}_lastUpdatedDate eq '2019-08-10'
  </code></pre>
  
  <p>This returns 400 error saying that <code>extension_{Id}_lastUpdatedDate</code> does not exist</p>
  
  <pre><code>{
    "error": {
      "code": "Request_UnsupportedQuery",
      "message": "Property 'extension_{Id}_lastUpdatedDate' does not exist as a declared property or extension property.",
      "innerError": {
        "request-id": "a925b2f4-fef8-47a1-b644-9b2e652f1746",
        "date": "2019-09-13T14:14:00"
      }
    }
  }
  </code></pre>
  
  <p>However, when I sent exactly the same request, just except the filter part of the query, like this</p>
  
  <pre><code>https://graph.microsoft.com/v1.0/users?$select=extension_{Id}_lastUpdatedDate
  </code></pre>
  
  <p>I receive 200 with the results, which sounds like the field exists and is correctly filled for all users in AD</p>
  
  <pre><code>{
      "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#users(extension_{Id}_lastUpdatedDate)",
      "value": [
          {"extension_{Id}_lastUpdatedDate": "2018-07-12T14:31:47.208Z"}, 
          {"extension_{Id}_lastUpdatedDate": "2018-05-30T14:28:47.208Z"}, 
          {"extension_{Id}_lastUpdatedDate": "2018-06-30T14:28:47.208Z"}, 
          {"extension_{Id}_lastUpdatedDate": "2018-07-30T14:28:47.208Z"}, 
          {"extension_{Id}_lastUpdatedDate": "2018-08-30T14:28:47.208Z"}, 
          {"extension_{Id}_lastUpdatedDate": "2018-07-12T14:31:47.208Z"}, 
          {"extension_{Id}_lastUpdatedDate": "2018-07-30T14:31:47.208Z"}, 
          {"extension_{Id}_lastUpdatedDate": "2018-07-30T14:31:47.208Z"}
      ]
  }
  </code></pre>
  
  <p>Does anyone know what's going on here? What the error message says sounds almost impossible to me, if I see the fields in a select query.</p>