title: Graphql Filter on Strapi using the "where" method to check if a record contain empty array
body: <p>Does anyone know how to use the graphql “where” filter method to check if an array contains any items?
  Currently, I use the following query:</p>
  
  <pre><code>query devices {
    onts(where:{images_null: false}){
      id
      images{
        id
      }
    }
  }
  </code></pre>
  
  <p>which returns:</p>
  
  <pre><code>{
    "data": {
      "onts": [
        {
          "id": "5ebfffa957c09c029fa7831c",
          "images": [
            {
              "id": "5ed3a5040889c464b4e5e07f"
            }
          ]
        },
        {
          "id": "5eccc3bb7c3b9d59351593de",
          "images": []
        },
        {
          "id": "5ece135e7c3b9d59351593df",
          "images": []
        }
      ]
    }
  }
  </code></pre>
  
  <p>As you can see, 2x of the returned records contain empty arrays.<br>
  I would like the query to only return records that contain at least one item in the array. </p>
  
  <p>Using Strapi v 3.0.1</p>
  
  <p>Appreciate any assistance. </p>