title: Adding @NotNull or Pattern constraints on List<String>
body: <p>How can we ensure the individual strings inside a list are not null/blank or follow  a specific pattern</p>
  
  <pre><code>@NotNull
  List&lt;String&gt; emailIds;
  </code></pre>
  
  <p>I also want to add a pattern</p>
  
  <p><code>@Pattern("\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b.")</code> </p>
  
  <p>but I can live without it.But I would definitely like to have a constraint which will check if any strings inside a list are null or blank. Also how would the Json schema look like</p>
  
  <pre><code>"ids": {
        "description": "The  ids associated with this.", 
      "type": "array",
          "minItems": 1,
          "items": {
          "type": "string",
           "required" :true }
   }
  
  "required" :true does not seem to do the job
  </code></pre>