title: Enforce object non emptyness using json schema
body: <p>We can enforce empty attribute of type object as follows:</p>
  
  <pre><code>{
     "description": "voice mail record",
     "type": "object",
     "additionalProperties": false,
     "properties": {}
  }
  </code></pre>
  
  <p>as explained <a href="https://stackoverflow.com/questions/3521135/enforce-empty-json-schema">here</a>.</p>
  
  <p>Now I want to validate attribute which</p>
  
  <ol>
  <li>is of object type,</li>
  <li>dont have any predefined properties</li>
  <li>can have properties of type string or numeric</li>
  <li>should not be empty</li>
  </ol>
  
  <p>Enforcing non-emptyness (point 4) is what I am unable to guess. This is somewhat opposite of enforcing emptyness as in above example. My current json schema excerpt looks like this:</p>
  
  <pre><code>"attribute": 
  {
      "type": "object",
      "additionalProperties": { "type": ["string","number","integer"] }
  }
  </code></pre>
  
  <p>But above does not enforce non-emptyness. How can I accomplish this?</p>