title: Ensure one property is not empty in JSON schema
body: <p>For the given schema below, is it possible to ensure that at least one property contains a value (ie, minLength is 1):</p>
  
  <pre><code>{
      "$schema": "http://json-schema.org/draft-04/schema#",
      "type": "object",
      "properties": {
          "fundRaiseId": {
              "type": "string"
          },
          "productTypeId": {
              "type": "string"
          },
          "businessLineId": {
              "type": "string"
          }
      }
  }
  </code></pre>
  
  <p>So this would pass validation:</p>
  
  <pre><code>{
   "fundRaiseId": "x"
  }
  </code></pre>
  
  <p>And this would fail as no values are present:</p>
  
  <pre><code>{
    "fundRaiseId": "",
    "productTypeId": "",
    "businessLineId": ""
  }
  </code></pre>