title: asana api listing unassigned tasks in a workspace
body: <p>I'd like to list all unassigned tasks in a given workspace using asana API. Tried using "assignee=null" as follows:</p>
  
  <pre><code>curl -u &lt;api-key&gt;: "https://app.asana.com/api/1.0/tasks?workspace=&lt;id&gt;&amp;assignee=null"
  </code></pre>
  
  <p>but it returns the error below:</p>
  
  <pre><code>{
    "errors": [
      {
        "message": "assignee: Not an email, ID, or \"me\": null"
      }
    ]
  }
  </code></pre>
  
  <p>Actually, any attempt to access tasks in a workspace without explicit assignee (me or assignee ID) fails, examples</p>
  
  <pre><code>curl -u &lt;api-id&gt;: "https://app.asana.com/api/1.0/tasks?workspace=&lt;wid&gt;&amp;due_on=null&amp;opt_pretty" 
  curl -u &lt;api-id&gt;: "https://app.asana.com/api/1.0/tasks?workspace=&lt;wid&gt;&amp;opt_fields=name,notes,assignee"
  </code></pre>
  
  <p>all return this error message</p>
  
  <pre><code>{
    "errors": [
      {
        "message": "assignee: Missing input"
      }
    ]
  }
  </code></pre>
  
  <p>Unassigned tasks do have a null assignee when I list them, which I can do for a project but not for a workspace:</p>
  
  <pre><code>curl -u &lt;api-key&gt;: "https://app.asana.com/api/1.0/projects/&lt;pid&gt;/tasks?opt_fields=name,assignee,notes"
  
  {
    "id": 123456789,
    "name": "watch asana vision talk",
    "assignee": null,
    "notes": "http://blog.asana.com/2011/02/asana-demo-vision-talk/"
  }
  </code></pre>
  
  <p>But I cannot list them from a project either since assignee options are ignored (see also <a href="https://stackoverflow.com/questions/10274798/asana-api-for-projects-assigned-to-me">Asana API for Projects Assigned to Me</a>)</p>
  
  <p>Am I missing something? Help appreciated! Thank you.</p>